An example of if in flatMap

UserServiceImpl.scala

  override def registerUser(): ServiceCall[requests.RegisterUser, UUID] = ServerServiceCall { req =>
    repository.emailHasBeenRegistered(req.email).flatMap { beenRegistered =>
      logger.debug(s"Email ${req.email} has been registered? $beenRegistered")
      if (!beenRegistered) {
        val id = UUID.randomUUID()
        logger.debug(s"Registering user $id")
        userEntityFor(id)
          .ask(InternalRegisterCommand(id, req.firstName, req.lastName, req.email, req.password))
      } else {
        logger.warn(s"Email ${req.email} has already been registered")
        throw EmailInUse(req.email)
      }
    }

  }