Java changes necessary for pkg_* rules

These changes are necessary to migrate pkg_library,
pkg_runfiles and pkg_directory to Starlark.

Part of Starlarkification fixit week.

RELNOTES:none
PiperOrigin-RevId: 390580467
diff --git a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/DebugPackageInfoApi.java b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/DebugPackageInfoApi.java
index d7a7246..7c61c2f 100644
--- a/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/DebugPackageInfoApi.java
+++ b/src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/DebugPackageInfoApi.java
@@ -48,7 +48,9 @@
   @StarlarkMethod(
       name = "stripped_file",
       doc = "Returns the stripped file (the explicit \".stripped\" target).",
+      allowReturnNones = true,
       structField = true)
+  @Nullable
   FileT getStrippedArtifact();
 
   @StarlarkMethod(