code: public String getResultKey() {
          Field singleField = getSingleField();
          if (singleField.getAlias() != null) {
              return singleField.getAlias();
          }
          return singleField.getName();
      }
docs: Returns the key of this MergedField for the overall result.
  This is either an alias or the field name.
  
  @return the key for this MergedField.