diff --git a/src/java_tools/import_deps_checker/java/com/google/devtools/build/importdeps/Main.java b/src/java_tools/import_deps_checker/java/com/google/devtools/build/importdeps/Main.java
index ac6defa..4d7f179 100644
--- a/src/java_tools/import_deps_checker/java/com/google/devtools/build/importdeps/Main.java
+++ b/src/java_tools/import_deps_checker/java/com/google/devtools/build/importdeps/Main.java
@@ -48,56 +48,54 @@
   /** Command line options. */
   public static class Options extends OptionsBase {
     @Option(
-      name = "input",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = ExistingPathConverter.class,
-      abbrev = 'i',
-      help = "Input jars with classes to check the completeness of their dependencies."
-    )
+        name = "input",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = ExistingPathConverter.class,
+        abbrev = 'i',
+        help = "Input jars with classes to check the completeness of their dependencies.")
     public List<Path> inputJars;
 
     @Option(
-      name = "directdep",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = ExistingPathConverter.class,
-      help = "Subset of Jars listed in --classpath_entry that --input Jars are allowed to depend "
-          + "on directly."
-    )
+        name = "directdep",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = ExistingPathConverter.class,
+        help =
+            "Subset of Jars listed in --classpath_entry that --input Jars are allowed to depend "
+                + "on directly.")
     public List<Path> directClasspath;
 
     @Option(
-      name = "classpath_entry",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = ExistingPathConverter.class,
-      help =
-          "Ordered classpath (Jar) to resolve symbols in the --input jars, like javac's -cp flag."
-    )
+        name = "classpath_entry",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = ExistingPathConverter.class,
+        help =
+            "Ordered classpath (Jar) to resolve symbols in the --input jars, like javac's -cp"
+                + " flag.")
     public List<Path> fullClasspath;
 
     @Option(
-      name = "bootclasspath_entry",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = ExistingPathConverter.class,
-      help =
-          "Bootclasspath that was used to compile the --input Jar with, like javac's "
-              + "-bootclasspath_entry flag (required)."
-    )
+        name = "bootclasspath_entry",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = ExistingPathConverter.class,
+        help =
+            "Bootclasspath that was used to compile the --input Jar with, like javac's "
+                + "-bootclasspath_entry flag (required).")
     public List<Path> bootclasspath;
 
     @Option(
@@ -130,22 +128,20 @@
     public String ruleLabel;
 
     @Option(
-      name = "checking_mode",
-      defaultValue = "WARNING",
-      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = CheckingModeConverter.class,
-      help = "Controls the behavior of the checker."
-    )
+        name = "checking_mode",
+        defaultValue = "WARNING",
+        documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = CheckingModeConverter.class,
+        help = "Controls the behavior of the checker.")
     public CheckingMode checkingMode;
 
     @Option(
-      name = "check_missing_members",
-      defaultValue = "true",
-      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      help = "Whether to check whether referenced fields and methods are defined."
-    )
+        name = "check_missing_members",
+        defaultValue = "true",
+        documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help = "Whether to check whether referenced fields and methods are defined.")
     public boolean checkMissingMembers;
   }
 
@@ -281,9 +277,7 @@
     }
   }
 
-  /**
-   * The checking mode of the dependency checker.
-   */
+  /** The checking mode of the dependency checker. */
   public enum CheckingMode {
     /** Emit 'errors' on missing or incomplete dependencies. */
     ERROR,
diff --git a/src/main/java/com/google/devtools/build/docgen/BuildEncyclopediaOptions.java b/src/main/java/com/google/devtools/build/docgen/BuildEncyclopediaOptions.java
index bfd5840..334e877 100644
--- a/src/main/java/com/google/devtools/build/docgen/BuildEncyclopediaOptions.java
+++ b/src/main/java/com/google/devtools/build/docgen/BuildEncyclopediaOptions.java
@@ -34,14 +34,13 @@
   public String productName;
 
   @Option(
-    name = "input_dir",
-    abbrev = 'i',
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help = "An input directory to read source files"
-  )
+      name = "input_dir",
+      abbrev = 'i',
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help = "An input directory to read source files")
   public List<String> inputDirs;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java b/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
index 2aea623..f9e2bad 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
@@ -67,7 +67,7 @@
   @Option(
       name = "extra_execution_platforms",
       converter = CommaSeparatedOptionListConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
       allowMultiple = true,
       effectTags = {OptionEffectTag.EXECUTION},
@@ -111,7 +111,7 @@
 
   @Option(
       name = "extra_toolchains",
-      defaultValue = "",
+      defaultValue = "null",
       converter = CommaSeparatedOptionListConverter.class,
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
       allowMultiple = true,
@@ -130,7 +130,7 @@
   @Option(
       name = "toolchain_resolution_override",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = {
         OptionEffectTag.AFFECTS_OUTPUTS,
@@ -204,7 +204,7 @@
   @Option(
       name = "experimental_add_exec_constraints_to_targets",
       converter = RegexFilterToLabelListConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
       effectTags = OptionEffectTag.LOADING_AND_ANALYSIS,
       allowMultiple = true,
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java b/src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java
index abd92bc..4e5dcf8 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java
@@ -86,7 +86,7 @@
   @Option(
       name = "define",
       converter = Converters.AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       allowMultiple = true,
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.CHANGES_INPUTS, OptionEffectTag.AFFECTS_OUTPUTS},
@@ -320,7 +320,7 @@
       name = "test_env",
       converter = Converters.OptionalAssignmentConverter.class,
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.TESTING,
       effectTags = {OptionEffectTag.TEST_RUNNER},
       help =
@@ -338,7 +338,7 @@
       name = "action_env",
       converter = Converters.OptionalAssignmentConverter.class,
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
       help =
@@ -354,7 +354,7 @@
       name = "repo_env",
       converter = Converters.OptionalAssignmentConverter.class,
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
       help =
@@ -497,7 +497,7 @@
   @Option(
       name = "experimental_action_listener",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       converter = LabelListConverter.class,
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.EXECUTION},
@@ -575,7 +575,7 @@
   @Option(
       name = "features",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.CHANGES_INPUTS, OptionEffectTag.AFFECTS_OUTPUTS},
       help =
@@ -590,7 +590,7 @@
       name = "target_environment",
       converter = LabelListConverter.class,
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.INPUT_STRICTNESS,
       effectTags = {OptionEffectTag.CHANGES_INPUTS},
       help =
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/test/TestConfiguration.java b/src/main/java/com/google/devtools/build/lib/analysis/test/TestConfiguration.java
index a120055..9520bc1 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/test/TestConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/test/TestConfiguration.java
@@ -139,17 +139,16 @@
     public boolean trimTestConfiguration;
 
     @Option(
-      name = "test_arg",
-      allowMultiple = true,
-      defaultValue = "",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      help =
-          "Specifies additional options and arguments that should be passed to the test "
-              + "executable. Can be used multiple times to specify several arguments. "
-              + "If multiple tests are executed, each of them will receive identical arguments. "
-              + "Used only by the 'bazel test' command."
-    )
+        name = "test_arg",
+        allowMultiple = true,
+        defaultValue = "null",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help =
+            "Specifies additional options and arguments that should be passed to the test "
+                + "executable. Can be used multiple times to specify several arguments. "
+                + "If multiple tests are executed, each of them will receive identical arguments. "
+                + "Used only by the 'bazel test' command.")
     public List<String> testArguments;
 
     @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptions.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptions.java
index b7e1fa4..95106c9 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptions.java
@@ -115,7 +115,7 @@
   @Option(
       name = "experimental_verify_repository_rules",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.INPUT_STRICTNESS,
       effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
       metadataTags = {OptionMetadataTag.EXPERIMENTAL},
diff --git a/src/main/java/com/google/devtools/build/lib/buildeventservice/BuildEventServiceOptions.java b/src/main/java/com/google/devtools/build/lib/buildeventservice/BuildEventServiceOptions.java
index 8dbf635..4b3062c 100644
--- a/src/main/java/com/google/devtools/build/lib/buildeventservice/BuildEventServiceOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/buildeventservice/BuildEventServiceOptions.java
@@ -83,17 +83,16 @@
   public String projectId;
 
   @Option(
-    name = "bes_keywords",
-    defaultValue = "",
-    converter = Converters.CommaSeparatedOptionListConverter.class,
-    documentationCategory = OptionDocumentationCategory.LOGGING,
-    effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
-    allowMultiple = true,
-    help =
-        "Specifies a list of notification keywords to be added the default set of keywords "
-            + "published to BES (\"command_name=<command_name> \", \"protocol_name=BEP\"). "
-            + "Defaults to none."
-  )
+      name = "bes_keywords",
+      defaultValue = "null",
+      converter = Converters.CommaSeparatedOptionListConverter.class,
+      documentationCategory = OptionDocumentationCategory.LOGGING,
+      effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
+      allowMultiple = true,
+      help =
+          "Specifies a list of notification keywords to be added the default set of keywords "
+              + "published to BES (\"command_name=<command_name> \", \"protocol_name=BEP\"). "
+              + "Defaults to none.")
   public List<String> besKeywords;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java b/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java
index 104c6bc..4c7384e 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java
@@ -139,18 +139,17 @@
   public boolean performExecutionPhase;
 
   @Option(
-    name = "output_groups",
-    converter = Converters.CommaSeparatedOptionListConverter.class,
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.OUTPUT_SELECTION,
-    effectTags = {OptionEffectTag.EXECUTION, OptionEffectTag.AFFECTS_OUTPUTS},
-    defaultValue = "",
-    help =
-        "Specifies which output groups of the top-level targets to build. If omitted, a default "
-            + "set of output groups are built. When specified the default set is overridden. "
-            + "However you may use --output_groups=+<output_group> or "
-            + "--output_groups=-<output_group> to instead modify the set of output groups."
-  )
+      name = "output_groups",
+      converter = Converters.CommaSeparatedOptionListConverter.class,
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.OUTPUT_SELECTION,
+      effectTags = {OptionEffectTag.EXECUTION, OptionEffectTag.AFFECTS_OUTPUTS},
+      defaultValue = "null",
+      help =
+          "Specifies which output groups of the top-level targets to build. If omitted, a default "
+              + "set of output groups are built. When specified the default set is overridden. "
+              + "However you may use --output_groups=+<output_group> or "
+              + "--output_groups=-<output_group> to instead modify the set of output groups.")
   public List<String> outputGroups;
 
   @Option(
@@ -252,7 +251,7 @@
       name = "experimental_multi_cpu",
       converter = Converters.CommaSeparatedOptionListConverter.class,
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
       metadataTags = {OptionMetadataTag.EXPERIMENTAL},
@@ -287,19 +286,18 @@
   public CacheBuilderSpec directoryCreationCacheSpec;
 
   @Option(
-    name = "aspects",
-    converter = Converters.CommaSeparatedOptionListConverter.class,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    allowMultiple = true,
-    help =
-        "Comma-separated list of aspects to be applied to top-level targets. All aspects "
-            + "are applied to all top-level targets independently. Aspects are specified in "
-            + "the form <bzl-file-label>%<aspect_name>, "
-            + "for example '//tools:my_def.bzl%my_aspect', where 'my_aspect' is a top-level "
-            + "value from from a file tools/my_def.bzl"
-  )
+      name = "aspects",
+      converter = Converters.CommaSeparatedOptionListConverter.class,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      allowMultiple = true,
+      help =
+          "Comma-separated list of aspects to be applied to top-level targets. All aspects "
+              + "are applied to all top-level targets independently. Aspects are specified in "
+              + "the form <bzl-file-label>%<aspect_name>, "
+              + "for example '//tools:my_def.bzl%my_aspect', where 'my_aspect' is a top-level "
+              + "value from from a file tools/my_def.bzl")
   public List<String> aspects;
 
   public BuildRequestOptions() throws OptionsParsingException {}
diff --git a/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionOptions.java b/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionOptions.java
index 71e9535..100def6 100644
--- a/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionOptions.java
@@ -85,7 +85,7 @@
       converter = Converters.StringToStringListConverter.class,
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = {OptionEffectTag.UNKNOWN},
-      defaultValue = "",
+      defaultValue = "null",
       allowMultiple = true,
       help =
           "The remote strategies to use for the given mnemonic. Passing 'remote'"
diff --git a/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java b/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java
index fdecd0b..1a1c1bc 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java
@@ -88,7 +88,7 @@
       name = "strategy",
       allowMultiple = true,
       converter = Converters.StringToStringListConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -105,7 +105,7 @@
       converter = RegexFilterAssignmentConverter.class,
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
-      defaultValue = "",
+      defaultValue = "null",
       help =
           "Override which spawn strategy should be used to execute spawn actions that have "
               + "descriptions matching a certain regex_filter. See --per_file_copt for details on"
diff --git a/src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java b/src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java
index 9c9f99f..4a9d9c5 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java
@@ -99,7 +99,7 @@
   @Option(
       name = "remote_header",
       converter = Converters.AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.REMOTE,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -112,7 +112,7 @@
   @Option(
       name = "remote_cache_header",
       converter = Converters.AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.REMOTE,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -126,7 +126,7 @@
   @Option(
       name = "remote_exec_header",
       converter = Converters.AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.REMOTE,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -140,7 +140,7 @@
   @Option(
       name = "remote_downloader_header",
       converter = Converters.AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.REMOTE,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
diff --git a/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java b/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java
index ee41872..a68aeb0 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java
@@ -57,13 +57,12 @@
     public String adb;
 
     @Option(
-      name = "adb_arg",
-      allowMultiple = true,
-      defaultValue = "",
-      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
-      help = "Extra arguments to pass to adb. Usually used to designate a device to install to."
-    )
+        name = "adb_arg",
+        allowMultiple = true,
+        defaultValue = "null",
+        documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+        effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
+        help = "Extra arguments to pass to adb. Usually used to designate a device to install to.")
     public List<String> adbArgs;
 
     @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftCommandLineOptions.java b/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftCommandLineOptions.java
index ffb9111..545f1af 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftCommandLineOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftCommandLineOptions.java
@@ -23,19 +23,18 @@
 /** Command-line options for building with Swift tools. */
 public class SwiftCommandLineOptions extends FragmentOptions {
   @Option(
-    name = "swiftcopt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
-    help = "Additional options to pass to Swift compilation."
-  )
+      name = "swiftcopt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
+      help = "Additional options to pass to Swift compilation.")
   public List<String> copts;
 
   @Option(
       name = "host_swiftcopt",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
       help = "Additional options to pass to swiftc for host tools.")
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java
index 4047d17..2c819fb 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java
@@ -266,73 +266,66 @@
   public boolean processHeadersInDependencies;
 
   @Option(
-    name = "copt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional options to pass to gcc."
-  )
+      name = "copt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional options to pass to gcc.")
   public List<String> coptList;
 
   @Option(
-    name = "cxxopt",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to gcc when compiling C++ source files."
-  )
+      name = "cxxopt",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to gcc when compiling C++ source files.")
   public List<String> cxxoptList;
 
   @Option(
-    name = "conlyopt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to gcc when compiling C source files."
-  )
+      name = "conlyopt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to gcc when compiling C source files.")
   public List<String> conlyoptList;
 
   @Option(
-    name = "linkopt",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to gcc when linking."
-  )
+      name = "linkopt",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to gcc when linking.")
   public List<String> linkoptList;
 
   @Option(
-    name = "ltoindexopt",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to the LTO indexing step (under --features=thin_lto)."
-  )
+      name = "ltoindexopt",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to the LTO indexing step (under --features=thin_lto).")
   public List<String> ltoindexoptList;
 
   @Option(
-    name = "ltobackendopt",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to the LTO backend step (under --features=thin_lto)."
-  )
+      name = "ltobackendopt",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to the LTO backend step (under --features=thin_lto).")
   public List<String> ltobackendoptList;
 
   @Option(
-    name = "stripopt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional options to pass to strip when generating a '<name>.stripped' binary."
-  )
+      name = "stripopt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional options to pass to strip when generating a '<name>.stripped' binary.")
   public List<String> stripoptList;
 
   @Option(
@@ -508,46 +501,44 @@
   public boolean saveTemps;
 
   @Option(
-    name = "per_file_copt",
-    allowMultiple = true,
-    converter = PerLabelOptions.PerLabelOptionsConverter.class,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help =
-        "Additional options to selectively pass to gcc when compiling certain files. "
-            + "This option can be passed multiple times. "
-            + "Syntax: regex_filter@option_1,option_2,...,option_n. Where regex_filter stands "
-            + "for a list of include and exclude regular expression patterns (Also see "
-            + "--instrumentation_filter). option_1 to option_n stand for "
-            + "arbitrary command line options. If an option contains a comma it has to be "
-            + "quoted with a backslash. Options can contain @. Only the first @ is used to "
-            + "split the string. Example: "
-            + "--per_file_copt=//foo/.*\\.cc,-//foo/bar\\.cc@-O0 adds the -O0 "
-            + "command line option to the gcc command line of all cc files in //foo/ "
-            + "except bar.cc."
-  )
+      name = "per_file_copt",
+      allowMultiple = true,
+      converter = PerLabelOptions.PerLabelOptionsConverter.class,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help =
+          "Additional options to selectively pass to gcc when compiling certain files. "
+              + "This option can be passed multiple times. "
+              + "Syntax: regex_filter@option_1,option_2,...,option_n. Where regex_filter stands "
+              + "for a list of include and exclude regular expression patterns (Also see "
+              + "--instrumentation_filter). option_1 to option_n stand for "
+              + "arbitrary command line options. If an option contains a comma it has to be "
+              + "quoted with a backslash. Options can contain @. Only the first @ is used to "
+              + "split the string. Example: "
+              + "--per_file_copt=//foo/.*\\.cc,-//foo/bar\\.cc@-O0 adds the -O0 "
+              + "command line option to the gcc command line of all cc files in //foo/ "
+              + "except bar.cc.")
   public List<PerLabelOptions> perFileCopts;
 
   @Option(
-    name = "per_file_ltobackendopt",
-    allowMultiple = true,
-    converter = PerLabelOptions.PerLabelOptionsConverter.class,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help =
-        "Additional options to selectively pass to LTO backend (under --features=thin_lto) when "
-            + "compiling certain backend objects. This option can be passed multiple times. "
-            + "Syntax: regex_filter@option_1,option_2,...,option_n. Where regex_filter stands "
-            + "for a list of include and exclude regular expression patterns. "
-            + "option_1 to option_n stand for arbitrary command line options. "
-            + "If an option contains a comma it has to be quoted with a backslash. "
-            + "Options can contain @. Only the first @ is used to split the string. Example: "
-            + "--per_file_ltobackendopt=//foo/.*\\.o,-//foo/bar\\.o@-O0 adds the -O0 "
-            + "command line option to the LTO backend command line of all o files in //foo/ "
-            + "except bar.o."
-  )
+      name = "per_file_ltobackendopt",
+      allowMultiple = true,
+      converter = PerLabelOptions.PerLabelOptionsConverter.class,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help =
+          "Additional options to selectively pass to LTO backend (under --features=thin_lto) when "
+              + "compiling certain backend objects. This option can be passed multiple times. "
+              + "Syntax: regex_filter@option_1,option_2,...,option_n. Where regex_filter stands "
+              + "for a list of include and exclude regular expression patterns. "
+              + "option_1 to option_n stand for arbitrary command line options. "
+              + "If an option contains a comma it has to be quoted with a backslash. "
+              + "Options can contain @. Only the first @ is used to split the string. Example: "
+              + "--per_file_ltobackendopt=//foo/.*\\.o,-//foo/bar\\.o@-O0 adds the -O0 "
+              + "command line option to the LTO backend command line of all o files in //foo/ "
+              + "except bar.o.")
   public List<PerLabelOptions> perFileLtoBackendOpts;
 
   @Option(
@@ -568,43 +559,39 @@
   public Label hostCrosstoolTop;
 
   @Option(
-    name = "host_copt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional options to pass to gcc for host tools."
-  )
+      name = "host_copt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional options to pass to gcc for host tools.")
   public List<String> hostCoptList;
 
   @Option(
-    name = "host_cxxopt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional options to pass to gcc for host tools."
-  )
+      name = "host_cxxopt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional options to pass to gcc for host tools.")
   public List<String> hostCxxoptList;
 
   @Option(
-    name = "host_conlyopt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to gcc when compiling C source files for host tools."
-  )
+      name = "host_conlyopt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to gcc when compiling C source files for host tools.")
   public List<String> hostConlyoptList;
 
   @Option(
-    name = "host_linkopt",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
-    help = "Additional option to pass to gcc when linking host tools."
-  )
+      name = "host_linkopt",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES, OptionEffectTag.AFFECTS_OUTPUTS},
+      help = "Additional option to pass to gcc when linking host tools.")
   public List<String> hostLinkoptList;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java
index 94c8249..29aec10 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaOptions.java
@@ -119,7 +119,7 @@
   @Option(
       name = "javacopt",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help = "Additional options to pass to javac.")
@@ -128,7 +128,7 @@
   @Option(
       name = "host_javacopt",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -139,7 +139,7 @@
   @Option(
       name = "jvmopt",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -364,7 +364,7 @@
   @Option(
       name = "extra_proguard_specs",
       allowMultiple = true,
-      defaultValue = "", // Ignored
+      defaultValue = "null",
       converter = LabelConverter.class,
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = {OptionEffectTag.UNKNOWN},
@@ -409,7 +409,7 @@
 
   @Option(
       name = "message_translations",
-      defaultValue = "",
+      defaultValue = "null",
       allowMultiple = true,
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
@@ -419,7 +419,7 @@
   @Option(
       name = "check_constraint",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help = "Check the listed constraint.")
@@ -547,7 +547,7 @@
       name = "plugin",
       converter = LabelListConverter.class,
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help = "Plugins to use in the build. Currently works with java_plugin.")
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcCommandLineOptions.java b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcCommandLineOptions.java
index 829cd02..f7457d9 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcCommandLineOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcCommandLineOptions.java
@@ -29,14 +29,13 @@
  */
 public class J2ObjcCommandLineOptions extends FragmentOptions {
   @Option(
-    name = "j2objc_translation_flags",
-    converter = Converters.CommaSeparatedOptionListConverter.class,
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help = "Additional options to pass to the J2ObjC tool."
-  )
+      name = "j2objc_translation_flags",
+      converter = Converters.CommaSeparatedOptionListConverter.class,
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help = "Additional options to pass to the J2ObjC tool.")
   public List<String> translationFlags;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java
index 4c5d7e7..b15f252 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcCommandLineOptions.java
@@ -100,13 +100,12 @@
   public boolean generateLinkmap;
 
   @Option(
-    name = "objccopt",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
-    effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
-    help = "Additional options to pass to Objective C compilation."
-  )
+      name = "objccopt",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
+      help = "Additional options to pass to Objective C compilation.")
   public List<String> copts;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
index dfe5e9e..052b62c 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
@@ -55,13 +55,12 @@
     public boolean generatedProtosInVirtualImports;
 
     @Option(
-      name = "protocopt",
-      allowMultiple = true,
-      defaultValue = "",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
-      help = "Additional options to pass to the protobuf compiler."
-    )
+        name = "protocopt",
+        allowMultiple = true,
+        defaultValue = "null",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
+        help = "Additional options to pass to the protobuf compiler.")
     public List<String> protocOpts;
 
     @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/ClientOptions.java b/src/main/java/com/google/devtools/build/lib/runtime/ClientOptions.java
index 431c4fb..7c442c9 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/ClientOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/ClientOptions.java
@@ -98,15 +98,14 @@
   }
 
   @Option(
-    name = "client_env",
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-    metadataTags = {OptionMetadataTag.HIDDEN},
-    effectTags = {OptionEffectTag.CHANGES_INPUTS},
-    converter = Converters.AssignmentConverter.class,
-    allowMultiple = true,
-    help = "A system-generated parameter which specifies the client's environment"
-  )
+      name = "client_env",
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      metadataTags = {OptionMetadataTag.HIDDEN},
+      effectTags = {OptionEffectTag.CHANGES_INPUTS},
+      converter = Converters.AssignmentConverter.class,
+      allowMultiple = true,
+      help = "A system-generated parameter which specifies the client's environment")
   public List<Map.Entry<String, String>> clientEnv;
 
   /**
@@ -116,26 +115,24 @@
    * <p>For example: "--default_override=rc:build=--cpu=piii"
    */
   @Option(
-    name = "default_override",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-    effectTags = {OptionEffectTag.CHANGES_INPUTS},
-    metadataTags = {OptionMetadataTag.HIDDEN},
-    converter = OptionOverrideConverter.class,
-    help = ""
-  )
+      name = "default_override",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {OptionEffectTag.CHANGES_INPUTS},
+      metadataTags = {OptionMetadataTag.HIDDEN},
+      converter = OptionOverrideConverter.class,
+      help = "")
   public List<OptionOverride> optionsOverrides;
 
   /** This is the filename that the Blaze client parsed. */
   @Option(
-    name = "rc_source",
-    defaultValue = "",
-    allowMultiple = true,
-    documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-    effectTags = {OptionEffectTag.CHANGES_INPUTS},
-    metadataTags = {OptionMetadataTag.HIDDEN},
-    help = ""
-  )
+      name = "rc_source",
+      defaultValue = "null",
+      allowMultiple = true,
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {OptionEffectTag.CHANGES_INPUTS},
+      metadataTags = {OptionMetadataTag.HIDDEN},
+      help = "")
   public List<String> rcSource;
 }
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/CommonCommandOptions.java b/src/main/java/com/google/devtools/build/lib/runtime/CommonCommandOptions.java
index 218dd2d..a9a9aac 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/CommonCommandOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/CommonCommandOptions.java
@@ -71,18 +71,17 @@
   public boolean enablePlatformSpecificConfig;
 
   @Option(
-    name = "config",
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    allowMultiple = true,
-    help =
-        "Selects additional config sections from the rc files; for every <command>, it "
-            + "also pulls in the options from <command>:<config> if such a section exists; "
-            + "if this section doesn't exist in any .rc file, Blaze fails with an error. "
-            + "The config sections and flag combinations they are equivalent to are "
-            + "located in the tools/*.blazerc config files."
-  )
+      name = "config",
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      allowMultiple = true,
+      help =
+          "Selects additional config sections from the rc files; for every <command>, it "
+              + "also pulls in the options from <command>:<config> if such a section exists; "
+              + "if this section doesn't exist in any .rc file, Blaze fails with an error. "
+              + "The config sections and flag combinations they are equivalent to are "
+              + "located in the tools/*.blazerc config files.")
   public List<String> configs;
 
   @Option(
@@ -206,7 +205,7 @@
   @Option(
       name = "build_metadata",
       converter = AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       allowMultiple = true,
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
@@ -495,18 +494,17 @@
   public ToolCommandLineEvent toolCommandLine;
 
   @Option(
-    name = "unconditional_warning",
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-    effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
-    allowMultiple = true,
-    help =
-        "A warning that will unconditionally get printed with build warnings and errors. This is "
-            + "useful to deprecate bazelrc files or --config definitions. If the intent is to "
-            + "effectively deprecate some flag or combination of flags, this is NOT sufficient. "
-            + "The flag or flags should use the deprecationWarning field in the option definition, "
-            + "or the bad combination should be checked for programmatically."
-  )
+      name = "unconditional_warning",
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
+      allowMultiple = true,
+      help =
+          "A warning that will unconditionally get printed with build warnings and errors. This is"
+              + " useful to deprecate bazelrc files or --config definitions. If the intent is to"
+              + " effectively deprecate some flag or combination of flags, this is NOT sufficient."
+              + " The flag or flags should use the deprecationWarning field in the option"
+              + " definition, or the bad combination should be checked for programmatically.")
   public List<String> deprecationWarnings;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/HostJvmStartupOptions.java b/src/main/java/com/google/devtools/build/lib/runtime/HostJvmStartupOptions.java
index 3677c7c..7a3ae9e 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/HostJvmStartupOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/HostJvmStartupOptions.java
@@ -39,14 +39,13 @@
   public String serverJavabase;
 
   @Option(
-    name = "host_jvm_args",
-    defaultValue = "", // NOTE: purely decorative!  See BlazeServerStartupOptions.
-    allowMultiple = true,
-    valueHelp = "<jvm_arg>",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help = "Flags to pass to the JVM executing Blaze."
-  )
+      name = "host_jvm_args",
+      defaultValue = "null", // NOTE: purely decorative!  See BlazeServerStartupOptions.
+      allowMultiple = true,
+      valueHelp = "<jvm_arg>",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help = "Flags to pass to the JVM executing Blaze.")
   public List<String> hostJvmArgs;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/commands/PrintActionCommand.java b/src/main/java/com/google/devtools/build/lib/runtime/commands/PrintActionCommand.java
index 4c4e2ae..4f9e458 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/commands/PrintActionCommand.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/commands/PrintActionCommand.java
@@ -84,15 +84,14 @@
    */
   public static class PrintActionOptions extends OptionsBase {
     @Option(
-      name = "print_action_mnemonics",
-      allowMultiple = true,
-      defaultValue = "",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      help =
-          "Lists which mnemonics to filter print_action data by, no filtering takes place "
-              + "when left empty."
-    )
+        name = "print_action_mnemonics",
+        allowMultiple = true,
+        defaultValue = "null",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help =
+            "Lists which mnemonics to filter print_action data by, no filtering takes place "
+                + "when left empty.")
     public List<String> printActionMnemonics = new ArrayList<>();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/sandbox/SandboxOptions.java b/src/main/java/com/google/devtools/build/lib/sandbox/SandboxOptions.java
index efe65ed..c56cf98 100644
--- a/src/main/java/com/google/devtools/build/lib/sandbox/SandboxOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/sandbox/SandboxOptions.java
@@ -133,48 +133,44 @@
   public boolean sandboxFakeUsername;
 
   @Option(
-    name = "sandbox_block_path",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help = "For sandboxed actions, disallow access to this path."
-  )
+      name = "sandbox_block_path",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help = "For sandboxed actions, disallow access to this path.")
   public List<String> sandboxBlockPath;
 
   @Option(
-    name = "sandbox_tmpfs_path",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help =
-        "For sandboxed actions, mount an empty, writable directory at this path"
-            + " (if supported by the sandboxing implementation, ignored otherwise)."
-  )
+      name = "sandbox_tmpfs_path",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help =
+          "For sandboxed actions, mount an empty, writable directory at this path"
+              + " (if supported by the sandboxing implementation, ignored otherwise).")
   public List<String> sandboxTmpfsPath;
 
   @Option(
-    name = "sandbox_writable_path",
-    allowMultiple = true,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help =
-        "For sandboxed actions, make an existing directory writable in the sandbox"
-            + " (if supported by the sandboxing implementation, ignored otherwise)."
-  )
+      name = "sandbox_writable_path",
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help =
+          "For sandboxed actions, make an existing directory writable in the sandbox"
+              + " (if supported by the sandboxing implementation, ignored otherwise).")
   public List<String> sandboxWritablePath;
 
   @Option(
-    name = "sandbox_add_mount_pair",
-    allowMultiple = true,
-    converter = MountPairConverter.class,
-    defaultValue = "",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help = "Add additional path pair to mount in sandbox."
-  )
+      name = "sandbox_add_mount_pair",
+      allowMultiple = true,
+      converter = MountPairConverter.class,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help = "Add additional path pair to mount in sandbox.")
   public List<ImmutableMap.Entry<String, String>> sandboxAdditionalMounts;
 
   @Option(
diff --git a/src/main/java/com/google/devtools/build/lib/worker/WorkerOptions.java b/src/main/java/com/google/devtools/build/lib/worker/WorkerOptions.java
index 6d7773b..8495b89 100644
--- a/src/main/java/com/google/devtools/build/lib/worker/WorkerOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/worker/WorkerOptions.java
@@ -101,7 +101,7 @@
 
   @Option(
       name = "high_priority_workers",
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
@@ -131,7 +131,7 @@
   @Option(
       name = "worker_extra_flag",
       converter = Converters.AssignmentConverter.class,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.UNKNOWN},
       help =
diff --git a/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java b/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java
index 345ae1a..d1635be 100644
--- a/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java
+++ b/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java
@@ -50,7 +50,7 @@
   @Option(
       name = "symbols",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = OptionEffectTag.UNKNOWN,
       help =
@@ -63,7 +63,7 @@
   @Option(
       name = "dep_roots",
       allowMultiple = true,
-      defaultValue = "",
+      defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
       effectTags = OptionEffectTag.UNKNOWN,
       help = "File path roots to search when resolving transitive bzl dependencies")
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/util/ConfigurationTestCase.java b/src/test/java/com/google/devtools/build/lib/analysis/util/ConfigurationTestCase.java
index 96051a6..e441fb0 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/util/ConfigurationTestCase.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/util/ConfigurationTestCase.java
@@ -73,14 +73,13 @@
 
   public static final class TestOptions extends OptionsBase {
     @Option(
-      name = "multi_cpu",
-      converter = Converters.CommaSeparatedOptionListConverter.class,
-      allowMultiple = true,
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.NO_OP},
-      defaultValue = "",
-      help = "Additional target CPUs."
-    )
+        name = "multi_cpu",
+        converter = Converters.CommaSeparatedOptionListConverter.class,
+        allowMultiple = true,
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.NO_OP},
+        defaultValue = "null",
+        help = "Additional target CPUs.")
     public List<String> multiCpus;
   }
 
diff --git a/src/test/java/com/google/devtools/common/options/OptionsParserTest.java b/src/test/java/com/google/devtools/common/options/OptionsParserTest.java
index 0b6e311..01e2baa 100644
--- a/src/test/java/com/google/devtools/common/options/OptionsParserTest.java
+++ b/src/test/java/com/google/devtools/common/options/OptionsParserTest.java
@@ -93,24 +93,22 @@
     public int bar;
 
     @Option(
-      name = "bing",
-      category = "one",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.NO_OP},
-      defaultValue = "",
-      allowMultiple = true
-    )
+        name = "bing",
+        category = "one",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.NO_OP},
+        defaultValue = "null",
+        allowMultiple = true)
     public List<String> bing;
 
     @Option(
-      name = "bang",
-      category = "one",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.NO_OP},
-      defaultValue = "",
-      converter = StringConverter.class,
-      allowMultiple = true
-    )
+        name = "bang",
+        category = "one",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.NO_OP},
+        defaultValue = "null",
+        converter = StringConverter.class,
+        allowMultiple = true)
     public List<String> bang;
 
     @Option(
diff --git a/src/test/java/com/google/devtools/common/options/TestOptions.java b/src/test/java/com/google/devtools/common/options/TestOptions.java
index d006240..3fbaa38 100644
--- a/src/test/java/com/google/devtools/common/options/TestOptions.java
+++ b/src/test/java/com/google/devtools/common/options/TestOptions.java
@@ -51,13 +51,12 @@
    */
 
   @Option(
-    name = "test_multiple_string",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.NO_OP},
-    defaultValue = "", // default value is ignored when allowMultiple=true.
-    allowMultiple = true,
-    help = "a repeatable string-valued flag with its own unhelpful help text"
-  )
+      name = "test_multiple_string",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.NO_OP},
+      defaultValue = "null",
+      allowMultiple = true,
+      help = "a repeatable string-valued flag with its own unhelpful help text")
   public List<String> testMultipleString;
 
   /*
@@ -65,16 +64,15 @@
    */
 
   @Option(
-    name = "test_list_converters",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.NO_OP},
-    defaultValue = "",
-    allowMultiple = true,
-    converter = ToListConverter.class,
-    help =
-        "a repeatable flag that accepts lists, but doesn't want to have lists of lists "
-            + "as a final type"
-  )
+      name = "test_list_converters",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.NO_OP},
+      defaultValue = "null",
+      allowMultiple = true,
+      converter = ToListConverter.class,
+      help =
+          "a repeatable flag that accepts lists, but doesn't want to have lists of lists "
+              + "as a final type")
   public List<String> testListConverters;
 
   /*
diff --git a/src/tools/android/java/com/google/devtools/build/android/AarGeneratorAction.java b/src/tools/android/java/com/google/devtools/build/android/AarGeneratorAction.java
index cb27c03..939dfaf 100644
--- a/src/tools/android/java/com/google/devtools/build/android/AarGeneratorAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/AarGeneratorAction.java
@@ -127,15 +127,14 @@
     public Path classes;
 
     @Option(
-      name = "proguardSpec",
-      defaultValue = "",
-      converter = ExistingPathConverter.class,
-      allowMultiple = true,
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      help = "Path to proguard spec file."
-    )
+        name = "proguardSpec",
+        defaultValue = "null",
+        converter = ExistingPathConverter.class,
+        allowMultiple = true,
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help = "Path to proguard spec file.")
     public List<Path> proguardSpecs;
 
     @Option(
diff --git a/src/tools/android/java/com/google/devtools/build/android/RClassGeneratorAction.java b/src/tools/android/java/com/google/devtools/build/android/RClassGeneratorAction.java
index b7acc95..fa4f41e 100644
--- a/src/tools/android/java/com/google/devtools/build/android/RClassGeneratorAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/RClassGeneratorAction.java
@@ -93,17 +93,16 @@
     public String packageForR;
 
     @Option(
-      name = "library",
-      allowMultiple = true,
-      defaultValue = "",
-      converter = DependencySymbolFileProviderConverter.class,
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      help =
-          "R.txt and manifests for the libraries in this binary's deps. We will write "
-              + "class files for the libraries as well. Expected format: lib1/R.txt[:lib2/R.txt]"
-    )
+        name = "library",
+        allowMultiple = true,
+        defaultValue = "null",
+        converter = DependencySymbolFileProviderConverter.class,
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help =
+            "R.txt and manifests for the libraries in this binary's deps. We will write "
+                + "class files for the libraries as well. Expected format: lib1/R.txt[:lib2/R.txt]")
     public List<DependencySymbolFileProvider> libraries;
 
     @Option(
diff --git a/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java b/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java
index 08ee82f..86691c9 100644
--- a/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/ResourceShrinkerAction.java
@@ -131,15 +131,14 @@
     public Path primaryManifest;
 
     @Option(
-      name = "dependencyManifest",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      converter = PathConverter.class,
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      help = "Paths to the manifests of the dependencies. Specify one path per flag."
-    )
+        name = "dependencyManifest",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        converter = PathConverter.class,
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help = "Paths to the manifests of the dependencies. Specify one path per flag.")
     public List<Path> dependencyManifests;
 
     @Option(
diff --git a/src/tools/android/java/com/google/devtools/build/android/ValidateAndLinkResourcesAction.java b/src/tools/android/java/com/google/devtools/build/android/ValidateAndLinkResourcesAction.java
index 1cd3821..d463586 100644
--- a/src/tools/android/java/com/google/devtools/build/android/ValidateAndLinkResourcesAction.java
+++ b/src/tools/android/java/com/google/devtools/build/android/ValidateAndLinkResourcesAction.java
@@ -59,7 +59,7 @@
         name = "compiledDep",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
-        defaultValue = "",
+        defaultValue = "null",
         converter = Converters.PathListConverter.class,
         category = "input",
         allowMultiple = true,
diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java b/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java
index 0353151..8dce30e 100644
--- a/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java
@@ -91,7 +91,7 @@
     @Option(
         name = "input",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         category = "input",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -105,7 +105,7 @@
     @Option(
         name = "classpath_entry",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         category = "input",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -118,7 +118,7 @@
     @Option(
         name = "bootclasspath_entry",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         category = "input",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -159,7 +159,7 @@
     @Option(
         name = "output",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         category = "output",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -279,7 +279,7 @@
     /** Type prefixes that we'll move to a custom package. */
     @Option(
         name = "rewrite_core_library_prefix",
-        defaultValue = "", // ignored
+        defaultValue = "null",
         allowMultiple = true,
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -289,7 +289,7 @@
     /** Interfaces whose default and static interface methods we'll emulate. */
     @Option(
         name = "emulate_core_library_interface",
-        defaultValue = "", // ignored
+        defaultValue = "null",
         allowMultiple = true,
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -299,7 +299,7 @@
     /** Members that we will retarget to the given new owner. */
     @Option(
         name = "retarget_core_library_member",
-        defaultValue = "", // ignored
+        defaultValue = "null",
         allowMultiple = true,
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -311,7 +311,7 @@
     /** Members not to rewrite. */
     @Option(
         name = "dont_rewrite_core_library_invocation",
-        defaultValue = "", // ignored
+        defaultValue = "null",
         allowMultiple = true,
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -321,7 +321,7 @@
     /** Converter functions from undesugared to desugared core library types. */
     @Option(
         name = "from_core_library_conversion",
-        defaultValue = "", // ignored
+        defaultValue = "null",
         allowMultiple = true,
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.UNKNOWN},
@@ -333,7 +333,7 @@
 
     @Option(
         name = "preserve_core_library_override",
-        defaultValue = "", // ignored
+        defaultValue = "null",
         allowMultiple = true,
         documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
         effectTags = {OptionEffectTag.UNKNOWN},
diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/scan/KeepScanner.java b/src/tools/android/java/com/google/devtools/build/android/desugar/scan/KeepScanner.java
index ab16407..9b03b04 100644
--- a/src/tools/android/java/com/google/devtools/build/android/desugar/scan/KeepScanner.java
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/scan/KeepScanner.java
@@ -68,7 +68,7 @@
     @Option(
         name = "classpath_entry",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
         converter = ExistingPathConverter.class,
@@ -80,7 +80,7 @@
     @Option(
         name = "bootclasspath_entry",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
         converter = ExistingPathConverter.class,
diff --git a/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileMerger.java b/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileMerger.java
index 8ecf6cc..2894b64 100644
--- a/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileMerger.java
+++ b/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileMerger.java
@@ -76,18 +76,18 @@
    */
   public static class Options extends OptionsBase {
     @Option(
-      name = "input",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = ExistingPathConverter.class,
-      abbrev = 'i',
-      help = "Input archives with .dex files to merge.  Inputs are processed in given order, so "
-          + "classes from later inputs will be added after earlier inputs.  Duplicate classes "
-          + "are dropped."
-    )
+        name = "input",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = ExistingPathConverter.class,
+        abbrev = 'i',
+        help =
+            "Input archives with .dex files to merge.  Inputs are processed in given order, so"
+                + " classes from later inputs will be added after earlier inputs.  Duplicate"
+                + " classes are dropped.")
     public List<Path> inputArchives;
 
     @Option(
diff --git a/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileSplitter.java b/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileSplitter.java
index 3f09471..78ab87d 100644
--- a/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileSplitter.java
+++ b/src/tools/android/java/com/google/devtools/build/android/dexer/DexFileSplitter.java
@@ -60,16 +60,15 @@
    */
   public static class Options extends OptionsBase {
     @Option(
-      name = "input",
-      allowMultiple = true,
-      defaultValue = "",
-      category = "input",
-      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-      effectTags = {OptionEffectTag.UNKNOWN},
-      converter = ExistingPathConverter.class,
-      abbrev = 'i',
-      help = "Input dex archive."
-    )
+        name = "input",
+        allowMultiple = true,
+        defaultValue = "null",
+        category = "input",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        converter = ExistingPathConverter.class,
+        abbrev = 'i',
+        help = "Input dex archive.")
     public List<Path> inputArchives;
 
     @Option(
diff --git a/src/tools/android/java/com/google/devtools/build/android/r8/DexFileMerger.java b/src/tools/android/java/com/google/devtools/build/android/r8/DexFileMerger.java
index d0ef675..0b7518c 100644
--- a/src/tools/android/java/com/google/devtools/build/android/r8/DexFileMerger.java
+++ b/src/tools/android/java/com/google/devtools/build/android/r8/DexFileMerger.java
@@ -110,7 +110,7 @@
     @Option(
         name = "input",
         allowMultiple = true,
-        defaultValue = "",
+        defaultValue = "null",
         documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
         effectTags = {OptionEffectTag.UNKNOWN},
         converter = ExistingPathConverter.class,
diff --git a/src/tools/remote/src/main/java/com/google/devtools/build/remote/worker/RemoteWorkerOptions.java b/src/tools/remote/src/main/java/com/google/devtools/build/remote/worker/RemoteWorkerOptions.java
index 78141a1..c6b876a 100644
--- a/src/tools/remote/src/main/java/com/google/devtools/build/remote/worker/RemoteWorkerOptions.java
+++ b/src/tools/remote/src/main/java/com/google/devtools/build/remote/worker/RemoteWorkerOptions.java
@@ -92,25 +92,23 @@
   public boolean sandboxing;
 
   @Option(
-    name = "sandboxing_writable_path",
-    defaultValue = "",
-    category = "build_worker",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    allowMultiple = true,
-    help = "When using sandboxing, allow running actions to write to this path."
-  )
+      name = "sandboxing_writable_path",
+      defaultValue = "null",
+      category = "build_worker",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      allowMultiple = true,
+      help = "When using sandboxing, allow running actions to write to this path.")
   public List<String> sandboxingWritablePaths;
 
   @Option(
-    name = "sandboxing_tmpfs_dir",
-    defaultValue = "",
-    category = "build_worker",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    allowMultiple = true,
-    help = "When using sandboxing, mount an empty tmpfs onto this path for each running action."
-  )
+      name = "sandboxing_tmpfs_dir",
+      defaultValue = "null",
+      category = "build_worker",
+      documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      allowMultiple = true,
+      help = "When using sandboxing, mount an empty tmpfs onto this path for each running action.")
   public List<String> sandboxingTmpfsDirs;
 
   @Option(