code: @Nullable
    public static ZonedDateTime getWithMillisOnly (@Nullable final ZonedDateTime aODT)
    {
      return aODT == null ? null : aODT.withNano (aODT.get (ChronoField.MILLI_OF_SECOND) *
                                                  (int) CGlobal.NANOSECONDS_PER_MILLISECOND);
    }
docs: Get the passed date time but with micro and nanoseconds set to 0, so that
  only the milliseconds part is present. This is helpful for XSD
  serialization, where only milliseconds granularity is available.
  
  @param aODT
  Source date time. May be <code>null</code>.
  @return <code>null</code> if the parameter is <code>null</code>, the local
  date time with microseconds and nanoseconds set to 0 otherwise.
  @since 9.2.0