code: @Deprecated
    public void addDeltaField(String... deltaFieldName) {
      StringBuilder sb = new StringBuilder(getProp(ConfigurationKeys.EXTRACT_DELTA_FIELDS_KEY, ""));
      Joiner.on(",").appendTo(sb, deltaFieldName);
      setProp(ConfigurationKeys.EXTRACT_DELTA_FIELDS_KEY, sb.toString());
    }
docs: Add more delta fields to the existing set of delta fields.
  
  @param deltaFieldName delta field names
  @deprecated It is recommended to add delta fields in {@code WorkUnit} instead of {@code Extract}.