protected function setFrequencyTypeAttr($value = null, $isDirty = true)
    {
        if (!is_null($value)) {
            if (!in_array($value, self::$frequencyTypes)) {
                throw new Exception('Invalid frequencyType');
            }
            $this->frequencyType = $value;
            $this->setDirtyState($isDirty, 'frequencyType');
        }
    }