public function setOperator($pOperator)
    {
        if (empty($pOperator)) {
            $pOperator = self::AUTOFILTER_COLUMN_RULE_EQUAL;
        }
        if ((!in_array($pOperator, self::$operators)) &&
            (!in_array($pOperator, self::$topTenValue))) {
            throw new PhpSpreadsheetException('Invalid operator for column AutoFilter Rule.');
        }
        $this->operator = $pOperator;

        return $this;
    }