code: public static String localDateTimeToString(LocalDateTime value, String emptyTimeString) {
          return (value == null) ? emptyTimeString : value.toString();
      }
docs: localDateTimeToString, This will return the supplied LocalDateTime as a string. If the value
  is null, this will return the value of emptyTimeString. Time values will be output in the
  same format as LocalDateTime.toString().
  
  Javadocs from LocalDateTime.toString():
  
  Outputs this date-time as a {@code String}, such as {@code 2007-12-03T10:15:30}.
  <p>
  The output will be one of the following ISO-8601 formats:
  <ul>
  <li>{@code uuuu-MM-dd'T'HH:mm}</li>
  <li>{@code uuuu-MM-dd'T'HH:mm:ss}</li>
  <li>{@code uuuu-MM-dd'T'HH:mm:ss.SSS}</li>
  <li>{@code uuuu-MM-dd'T'HH:mm:ss.SSSSSS}</li>
  <li>{@code uuuu-MM-dd'T'HH:mm:ss.SSSSSSSSS}</li>
  </ul>
  The format used will be the shortest that outputs the full value of the time where the
  omitted parts are implied to be zero.