Mark BlazeModule#getPackageSettings @Nullable

RELNOTES: None
PiperOrigin-RevId: 320218301
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java
index bb7eb77..8c44dfd 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java
@@ -400,6 +400,7 @@
    *
    * <p>Note that only one helper per Bazel/Blaze runtime is allowed.
    */
+  @Nullable
   public PackageSettings getPackageSettings() {
     return null;
   }