code: @VisibleForTesting
    @GwtIncompatible("Unnecessary")
    String expandSourceMapPath(B options, JSModule forModule) {
      if (Strings.isNullOrEmpty(options.sourceMapOutputPath)) {
        return null;
      }
      return expandCommandLinePath(options.sourceMapOutputPath, forModule);
    }
docs: Expansion function for source map.