ارور Call to a member function course() on null

باسلام،
در دوره آموزشی ساخت فروشگاه، ارور زیر رو دریافت میکنم.

کد کنترولر :

<?php

namespace AppHttpControllersadmin;

use AppCourse;
use AppHttpRequestsCourseRequest;
use IlluminateHttpRequest;
use AppHttpControllersController;

class CourseController extends AdminController
{
    /**
     * Display a listing of the resource.
     *
     * @return IlluminateHttpResponse
     */
    public function index()
    {
        $courses = Course::latest()->paginate(20);
        return view('admin.courses.all' , compact('courses'));
    }

    /**
     * Show the form for creating a new resource.
     *
     * @return IlluminateHttpResponse
     */
    public function create()
    {
        return view('admin.courses.create');
    }

    /**
     * Store a newly created resource in storage.
     *
     * @param CourseRequest|Request $request
     * @return IlluminateHttpResponse
     */
    public function store(CourseRequest $request)
    {
        $imagesUrl = $this->uploadImages($request->file('images'));
        auth()->user()->course()->create(array_merge($request->all() , [ 'images' => $imagesUrl]));

        return redirect(route('courses.index'));
    }

    /**
     * Display the specified resource.
     *
     * @param  AppCourse  $course
     * @return IlluminateHttpResponse
     */
    public function show(Course $course)
    {
        //
    }

    /**
     * Show the form for editing the specified resource.
     *
     * @param  AppCourse  $course
     * @return IlluminateHttpResponse
     */
    public function edit(Course $course)
    {
        return view('admin.courses.edit' , compact('course'));
    }

    /**
     * Update the specified resource in storage.
     *
     * @param  IlluminateHttpRequest  $request
     * @param  AppCourse  $course
     * @return IlluminateHttpResponse
     */
    public function update(Request $request, Course $course)
    {
    }

    /**
     * Remove the specified resource from storage.
     *
     * @param  AppCourse  $course
     * @return IlluminateHttpResponse
     */
    public function destroy(Course $course)
    {
        $course->delete();
        return redirect(route('courses.index'));
    }
}