unable to generate token using socialite login

[sadeqsafaeian]

to login from socialite
Argument 1 passed to Tymon\JWTAuth\JWTGuard::login() must implement interface Tymon\JWTAuth\Contracts\JWTSubject, null given, called in C:\wamp64\www\.....Controllers\Auth\OAuthController.php on line 48

      $this->guard()->setToken(
            $token = $this->guard()->login($user)
        );

what's the solution؟