public TileArchiveMetadata setExtraMetadata(String key, Object value) {
    if (key != null && value != null) {
      others.put(key, value.toString());
    }
    return this;
  }
Sets an extra metadata entry in {@link #others}.
planetiler-core/src/main/java/com/onthegomap/planetiler/archive/TileArchiveMetadata.java