为什么我的模型在serviceRepository laravel中不起作用

我这里有一个服务提供商，还有 http://dfg.gd/blog/decoupling-your-code-in-laravel-using-repositiories-and-services我的服务提供商：

class UsersRepositoryServiceProvider extends ServiceProvider
{
    public function register()
    {
        $this->app->bind('App'Repositories'Users'UsersInterface', function($app)
        {
            return new UsersRepository(new User);
        });
    }

我得到错误：Call to a member function find() on a non-object 我的仓库：

use 'Illuminate'Database'Eloquent'Model;
//..
protected $usersModel;
public function __consturct(Model $users)
{
    $this->usersModel = $users;
}
/**
 * Get user by id
 * 
 * @param mixed $userId
 * @return Model
 */
public function getUserById($userId)
{
    return $this->convertFormat($this->usersModel->find($userId));
}