code: func (b *builtinUTCTimestampWithoutArgSig) evalTime(row chunk.Row) (types.Time, bool, error) {
  	result, isNull, err := evalUTCTimestampWithFsp(b.ctx, 0)
  	return result, isNull, err
  }
docs: // evalTime evals UTC_TIMESTAMP().
  // See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_utc-timestamp