Check that custom package is not null in android_local_test before pu…

…tting it into the robolectric properties file.

This is incidentally what Starlark android_local_test does: https://github.com/bazelbuild/rules_android/blob/0c605a44587219016248ff5702331c88b805cc01/rules/android_local_test/impl.bzl#L199

Fixes #21632.

PiperOrigin-RevId: 615451196
Change-Id: I98adef9be42d89e25188f3d9204b466e780e2945

src/main/java/com/google/devtools/build/lib/rules/android/AndroidLocalTestBase.java

@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.rules.android;
 
+import static com.google.common.base.Strings.nullToEmpty;
 import static com.google.devtools.build.lib.rules.java.DeployArchiveBuilder.Compression.COMPRESSED;
 
 import com.google.common.collect.ImmutableList;
@@ -162,9 +163,9 @@ public ConfiguredTarget create(RuleContext ruleContext)
         Substitution.of("%android_merged_resources%", "jar:file:" + resourcesLocation + "!/res"));
     substitutions.add(
         Substitution.of("%android_merged_assets%", "jar:file:" + resourcesLocation + "!/assets"));
-    substitutions.add(
-        Substitution.of(
-            "%android_custom_package%", resourceApk.getValidatedResources().getJavaPackage()));
+
+    String customPackage = resourceApk.getValidatedResources().getJavaPackage();
+    substitutions.add(Substitution.of("%android_custom_package%", nullToEmpty(customPackage)));
 
     substitutions.add(
         Substitution.of(