Laravel 5.3 LoginController - Header may not contain more than a single header, new line detected

I have a problem when changing the default LoginController redirect after login, I'm getting an ErrorException in Response.php line 339: Header may not contain more than a single header, new line detected

I have already tried everything but it just does not work, the code is:

class LoginController extends Controller
{

protected $redirectTo = '/home';

protected function redirectTo()
{
    if (\Auth::check()) {
       $user_id = \Auth::id();
       $usuario = users::where('id','=',$user_id)->first();
       if($usuario->hasRole('copy')){
           return redirect('/copy/dashboardCopy');
        }
    } 
}

/**
 * Create a new controller instance.
 *
 * @return void
 */
public function __construct()
{
    $this->middleware('guest', ['except' => 'logout']);
}
}

According to Laravel documentation, the method has higher priority than the attribute, so I assume it's okay to leave the class attribute as it is.

And also, I have already checked, and the code is actually reaching the last condition.

The method redirectTo should return an url path, not the Redirect response.

...
protected function redirectTo()
{
    if(\Auth::user()->hasRole('copy')){
        return '/copy/dashboardCopy';
    }       
}
...