protected function checkRequired($element, $schema)
{
$ignore = isset(static::$ignoreRequiredVal[$schema->getObjectName()]) ? static::$ignoreRequiredVal[$schema->getObjectName()] : [];
foreach (array_diff_key(array_flip($schema->required), (array) $element, array_flip($ignore)) as $key => $value) {
$this->appendError($key, 'this element is required.');
}
}