Don't dereference a null pointer

If we don't specifiy an output for R.java, don't try to write
data to the class definition

Change-Id: I3ad471ec93dcb8baf13f221174065679cce311ad
Fixes: 72547268
Test: out/host/linux-x86/nativetest64/aapt2_tests/aapt2_tests

tools/aapt2/java/JavaClassGenerator_test.cpp

@@ -438,4 +438,22 @@ TEST(JavaClassGeneratorTest, GenerateOnResourcesLoadedCallbackForSharedLibrary)
   EXPECT_THAT(output, HasSubstr("com.boo.R.onResourcesLoaded"));
 }
 
+TEST(JavaClassGeneratorTest, OnlyGenerateRText) {
+  std::unique_ptr<ResourceTable> table =
+      test::ResourceTableBuilder()
+          .SetPackageId("android", 0x01)
+          .AddValue("android:attr/foo", ResourceId(0x01010000), util::make_unique<Attribute>())
+          .AddValue("android:styleable/hey.dude", ResourceId(0x01020000),
+                    test::StyleableBuilder()
+                        .AddItem("android:attr/foo", ResourceId(0x01010000))
+                        .Build())
+          .Build();
+
+  std::unique_ptr<IAaptContext> context =
+      test::ContextBuilder().SetPackageId(0x01).SetCompilationPackage("android").Build();
+  JavaClassGenerator generator(context.get(), table.get(), {});
+
+  ASSERT_TRUE(generator.Generate("android", nullptr));
+}
+
 }  // namespace aapt