Laravel 5.2 send activation link and default registration

In Laravel AuthController with in create function ,after successfull registration i want to send activation code to user registered email id. After registration i checked it with echo"testing..." but it throws error like this

ErrorException in SessionGuard.php line 439:
Argument 1 passed to Illuminate\Auth\SessionGuard::login() must implement interface Illuminate\Contracts\Auth\Authenticatable, null given, called in C:\xampp\htdocs\sdeal\vendor\laravel\framework\src\Illuminate\Foundation\Auth\RegistersUsers.php on line 63 and defined

Authcontroller:

<?php

namespace App\Http\Controllers\Admin\Auth;

use App\Modules\Models\User\User;
use Illuminate\Http\Request;
use Validator;
use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\ThrottlesLogins;
use Illuminate\Foundation\Auth\AuthenticatesAndRegistersUsers;

class AuthController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Registration & Login Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles the registration of new users, as well as the
    | authentication of existing users. By default, this controller uses
    | a simple trait to add these behaviors. Why don't you explore it?
    |
    */

    use AuthenticatesAndRegistersUsers, ThrottlesLogins;

    /**
     * Where to redirect users after login / registration.
     *
     * @var string
     */
    protected $redirectTo = '/user';

    protected $redirectAfterLogout = '/user/register';

    protected $loginView = 'admin.auth.login';

    protected $registerView = 'admin.auth.register';

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

    /**
     * Get a validator for an incoming registration request.
     *
     * @param  array  $data
     * @return \Illuminate\Contracts\Validation\Validator
     */
    protected function validator(array $data)
    {
        return Validator::make($data, [
            'name' => 'required|max:255',
            'email' => 'required|email|max:255|unique:users',
            'password' => 'required|min:6|confirmed',
        ]);
    }

    /**
     * Create a new user instance after a valid registration.
     *
     * @param  array  $data
     * @return User
     */
    protected function create(array $data)
    {
        $user= User::create([
            'name' => $data['name'],
            'email' => $data['email'],
            'password' => bcrypt($data['password']),
           'code'=> str_random(30),
        ]);
        //send email with activation code
        echo "testing";
        // Mail::send('email.verify', $confirmation_code, function($message) {
        //     $message->to(Input::get('email'), Input::get('username'))
        //         ->subject('Verify your email address');
        // });

    }


    /**
     * Get the needed authorization credentials from the request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return array
     */
    protected function getCredentials(Request $request)
    {
        $request = $request->only($this->loginUsername(), 'password');
//        $request['type'] = config('constants.type_superuser');

        return $request;
    }
}

How can i solve this error