public SearchSourceBuilder fields(String... fields){
  if (fieldNames == null) {
    fieldNames=new ArrayList<>();
  }
  Collections.addAll(fieldNames,fields);
  return this;
}

public SearchSourceBuilder fields ( String ... fields ) { if ( fieldNames == null ) { fieldNames = new ArrayList < > ( ) ; } Collections . addAll ( fieldNames , fields ) ; return this ; }
adds the fields to load and return as part of the search request . if none are specified , the source of the document will be returned .
