code: @Nullable
    public static LocalDateTime getWithMillisOnly (@Nullable final LocalDateTime aLDT)
    {
      return aLDT == null ? null : aLDT.withNano (aLDT.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 aLDT
  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