Fuel\Validation\Rule\Required::validate PHP Method

    public function validate($value, $field = null, $allFields = null)
    {
        // Make sure the array key exists in the data
        // This check will only be performed if $field and $allFields are set. Else only the value passed will be tested
        if ($field === null or $allFields !== null and !isset($allFields[$field])) {
            return false;
        }
        return $value === 0 or $value === false or !empty($value) or $value === '0';
    }