code: @VisibleForTesting
    static Map<String, String> encodeMetadata(Map<String, byte[]> metadata) {
      return Maps.transformValues(metadata, ENCODE_METADATA_VALUES);
    }
docs: Helper for converting from a Map&lt;String, byte[]&gt; metadata map that may be in a
  StorageObject into a Map&lt;String, String&gt; suitable for placement inside a
  GoogleCloudStorageItemInfo.