title: OAuth error "Trying to access array offset on value of type null" using Socialite
body: <p>I making OAuth using Laravel Socialite, step by step i trying 3 different guides and result the same error <code>Trying to access array offset on value of type null</code>. </p>
  
  <p>My composer.json</p>
  
  <pre><code>"require": {
          "php": "^7.3.1",
          "fideloper/proxy": "^4.0",
          "laravel/framework": "^6.2",
          "laravel/socialite": "^4.3",
          "laravel/tinker": "^2.0",
          "laravel/ui": "^1.2",
          "socialiteproviders/vkontakte": "^4.0"
      },
  </code></pre>
  
  <p>Also my LoginController</p>
  
  <pre><code>public function redirectToProvider()
      {
          return Socialite::driver('github')-&gt;redirect();
      }
  
      public function handleProviderCallback()
      {
          $user = Socialite::driver('github')-&gt;user();
  
          dd($user);
      }
  </code></pre>