code: public final Timestamp addMillis(long amount)
      {
          if (amount == 0 && _precision.includes(Precision.SECOND) && _fraction != null && _fraction.scale() >= 3) {
              // Zero milliseconds are to be added, and the precision does not need to be increased.
              return this;
          }
          return addMillisForPrecision(amount, Precision.SECOND, true);
      }
docs: Returns a timestamp relative to this one by the given number of
  milliseconds.
  <p>
  This method always returns a Timestamp with SECOND precision and a seconds
  value precise at least to the millisecond. For example, adding one millisecond
  to {@code 2011T} results in {@code 2011-01-01T00:00:00.001-00:00}. To receive
  a Timestamp that always maintains the same precision as the original, use
  {@link #adjustMillis(long)}.
  milliseconds.
  
  @param amount a number of milliseconds.