code: @Override
      public String getStr4DateTime(final ReadableDateTime _value)
      {
          String ret;
          if (_value.getEra() == 0) {
              ret = _value.toDateTime().minusYears(1).toString(ISODateTimeFormat.dateHourMinuteSecondFraction());
              ret = ret.substring(1) + " BC";
          } else {
              ret = _value.toDateTime().toString(ISODateTimeFormat.dateHourMinuteSecondFraction());
          }
          return ret;
      }
docs: {@inheritDoc}.
  <br/>
  Postgres does not work with the year "ZERO" therefore the year
  is translated like a Gregorian/Julian Calendar (ZERO = -1)