I recently updated a Swift 2.0 project to Swift 3.0, and now I have this error with my Firebase signUp function (the code definitely worked before). 

```
func signUp(_ email: String, username: String, password: String, data: Data!) {

    Auth.auth().createUser(withEmail: email, password: password, completion: { (user, error) in

        if error == nil {

            // error here
            self.setUserInfo(user, username: username, password: password, data: data)
        }else {
            print(error!.localizedDescription)
        }
    })
}

```

I am very grateful for any assistance with this.

**Thanks!**