Laravel\Passport\Client returns null instance - php

Question

My Auth API was working but now it gives error. I can register successfully but I cant get the return of the login token because I get an error:
TypeError: Argument 1 passed to App\Http\Controllers\UserController::getTokenAndRefreshToken() must be an instance of Laravel\Passport\Client, null given, called in /var/www/laravel/app/Http/Controllers/UserController.php on line 44 in file /var/www/laravel/app/Http/Controllers/UserController.php on line 47
Like I said, it was working before, I just added another model and created one-to-many relationship with user model but I don't think that has got anything to do with Passport.
Why I get a null object from OClient::where('password_client', 1)->first();
I create user like this in UserController's register method.
$user = User::create($input);
$oClient = OClient::where('password_client', 1)->first();
return $this->getTokenAndRefreshToken($oClient, $user->email, $password);
public function getTokenAndRefreshToken(OClient $oClient, $email, $password) {
$oClient = OClient::where('password_client', 1)->first();
$http = new Client;
$response = $http->request('POST', '/oauth/token', [
'form_params' => [
'grant_type' => 'password',
'client_id' => $oClient->id,
'client_secret' => $oClient->secret,
'username' => $email,
'password' => $password,
'scope' => '*',
],
]);
$result = json_decode((string) $response->getBody(), true);
return response()->json($result, $this->successStatus);
}