code: protected function getModelInstance(string $mailableClass, string $argumentName, Model $model, $id): Model
      {
          $modelInstance = $id ? $model->find($id) : $model->first();
  
          if (! $modelInstance) {
              throw CouldNotDetermineValue::noModelInstanceFound($model);
          }
  
          return $modelInstance;
      }
docs: @param string $mailableClass
  @param string $argumentName
  @param \Illuminate\Database\Eloquent\Model $model
  @param string|int|null $id
  
  @return \Illuminate\Database\Eloquent\Model
  @throws \Spatie\MailableTest\Exceptions\CouldNotDetermineValue