RequiredField::validate

public function validate(array $fields): Result
{
	$result = new Result();

	if (!array_key_exists($this->fieldToCheck, $fields))
	{
		$result->addError(new Error(
			Loc::getMessage('CRM_DTO_VALIDATOR_FIELD_IS_REQUIRED', [
				'#FIELD#' => $this->fieldToCheck,
				'#PARENT_OBJECT#' => $this->dto->getName(),
			]),
			'FIELD_IS_REQUIRED',
			[
				'FIELD' => $this->fieldToCheck,
				'PARENT_OBJECT' => $this->dto->getName(),
			]
		));
	}

	return $result;
}