code: public function validate($gender, Constraint $constraint)
      {
          if (null === $gender) {
              return;
          }
  
          if (!$constraint instanceof Gender) {
              throw new UnexpectedTypeException($constraint, Gender::class);
          }
  
          if (!call_user_func($this->genderClass.'::isValid', $gender)) {
              $this->context
                  ->buildViolation($constraint->invalid_gender)
                  ->addViolation();
          }
      }
docs: {@inheritdoc}