public async Task <IEnumerable <Course> > GetCoursesByIdAsync(
     [ID(nameof(Course))] Guid[] ids,
     CourseByIdDataLoader courseByIdDataLoader,
     CancellationToken cancellationToken) => await courseByIdDataLoader.LoadAsync(ids, cancellationToken)
 ?? Array.Empty <Course>();
 public Task <Course?> GetCourseByIdAsync(
     [ID(nameof(Course))] Guid id,
     CourseByIdDataLoader courseByIdDataLoader,
     CancellationToken cancellationToken) => courseByIdDataLoader.LoadAsync(id, cancellationToken) !;