/**
  * @param RegistrationFlow $value The value that should be validated
  * @return void
  * @throws InvalidValidationOptionsException
  */
 protected function isValid($value)
 {
     /** @noinspection PhpUndefinedMethodInspection */
     $existingAccount = $this->accountRepository->findOneByAccountIdentifier($value->getEmail());
     if ($existingAccount) {
         // todo: error message translatable
         $this->result->forProperty('email')->addError(new Error('Die Email-Adresse %s wird bereits verwendet!', 1336499566, [$value->getEmail()]));
     }
     // If a custom validation service is registered, call its validate method to allow custom validations during registration
     if ($this->objectManager->isRegistered(RegistrationFlowValidationServiceInterface::class)) {
         $instance = $this->objectManager->get(RegistrationFlowValidationServiceInterface::class);
         $instance->validateRegistrationFlow($value, $this);
     }
 }