static Source createSource(
     final String key, final SourceType type, final Map<String, String> fields) {
   Source source = new Source();
   source.key = key;
   source.type = type;
   source.fields = fields;
   return source;
 }
 static Source createSource(final String key, final SourceType type) {
   Source source = new Source();
   source.key = key;
   source.type = type;
   return source;
 }