public function getTypes()
    {
        if (!array_key_exists('value', $this->types)) {
            return;
        }

        //return an array, no matter one or many types defined
        if (is_array($this->types['value']) && count($this->types['value']) > 1) {
            return $this->types['value'];
        } else {
            return [$this->types['value']];
        }
    }