ErrorException in Validation

it's my first time making a log in laravel. I followed the steps here: https://scotch.io/tutorials/simple-and-easy-laravel-login-authentication. But this error comes out:

I'm really confused what this error is about since I'm new to laravel? Here is my controller code:

 public function login()
{
    $admins = Admin::all();
    $validator = \Validator::make($admins , ['username' => 'required', 'password' => 'required']);
    if ($validator->passes())
    {
        $userdata = array(
            'username' => Admin::get('username'),
            'password' => Admin::get('password'));
        if (Auth::attempt($userdata))
        {
            echo 'Success';
        }
        else {
            return Redirect::to('login');
        }
    }
}

Here is my route:

Route::resource('Admins','AdminController');
Route::post('login', array('uses' => 'AdminController@login'));

via Eymiєl Moralєs