未初始化的字符串偏移量:0 -初始值

我正在尝试检查会话:

<?php
namespace AndyJessop'Socialist'Http'Controllers;
use App'Http'Controllers'Controller;
use Illuminate'Http'Request;
use Illuminate'Http'Response;
use Illuminate'Auth'Guard;
use AndyJessop'Socialist'AuthenticateUser;
class AuthController extends Controller {
    public $auth;
    public function __construct(Guard $auth)
    {
       $this->auth = $auth;
    }
    public function login($provider, AuthenticateUser $authenticateUser, Request $request)
    {
        $user = $authenticateUser->execute($request->has('code'), $provider);
        return $user;
    }
    public function logout()
    {
        $this->auth->logout();
        return response()->json(['You have been logged out']);
    }
    public function checkSession()
    {
        $session = $this->auth->check();
        return $session;
    }
}

但是我得到错误:Uninitialized string offset: 0

这可能是什么原因?