code: public String toStringStrict() {
          LocalDateTime dateTime = getDateTimeStrict();
          String text = (dateTime == null) ? "" : dateTime.toString();
          return text;
      }
docs: toStringStrict, 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 or the time picker is
  null, then this will return an empty string ("").
  
  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.