code: public String toStringPermissive() {
          LocalDateTime dateTime = getDateTimePermissive();
          String text = (dateTime == null) ? "" : dateTime.toString();
          return text;
      }
docs: toStringPermissive, This returns a string representation of the values which are currently
  stored in the date and time picker. If the last valid value of the date picker is null, then
  this will return an empty string (""). If the last valid value of the time picker is null,
  then that portion of the time will be replaced with LocalTime.MIDNIGHT.
  
  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.