Post Error 500使用Eloquent添加新行

我正在尝试遵循一个教程，使社会网络，喜欢和不喜欢的功能，当没有行可用的数据库使用Ajax(添加一个新的条目)被打破。
我正在跟随教程-这个视频是他创建控制器的地方:
https://www.youtube.com/watch?v=drM19VKbCgU&list=PL55RiY5tL51oloSGk5XdO2MGjPqc0BxGV&index=20

开发环境:

• PhpStorm v9.0
• Xampp v3.2.2
jQuery v1.12.0
• 谷歌Chrome

错误图像:错误图片链接

The Whole cycle:
喜欢和不喜欢按钮(视图):

<a href="#" class="like">{{ Auth::user()->likes()->where('post_id', $post->id)->first() ?
Auth::user()->likes()->where('post_id', $post->id)->first()->like == 1 ?
'You like this post':'Like' : 'Like' }}</a> |
<a href="#" class="like">{{ Auth::user()->likes()->where('post_id', $post->id)->first() ?
 Auth::user()->likes()->where('post_id', $post->id)->first()->like == 0 ?    
'You don''t like this post':'Dislike' : 'Dislike' }}</a>
<script>
    var urlLike = '{{ route('like') }}';
</script>

路线:

Route::post('/like', [
   'uses' => 'PostController@postLikePost',
    'as' => 'like'
]);

listener + Ajax Call:

$('.like').on('click', function(event){
event.preventDefault();
postId = event.target.parentNode.parentNode.dataset['postid'];
var isLike = event.target.previousElementSibling == null;
//console.log(postId+' '+isLike);
$.ajax({
    method: 'POST',
    url: urlLike,
    data: {isLike: isLike, postId: postId, _token: token}
})
    .done(function(){
        console.log(event.target.innerText);
        event.target.innerText = isLike ? event.target.innerText == 'Like' ? 'You like this post':'Like' : event.target.innerText == 'Dislike' ? 'You don''t like this post':'Dislike' ;
        if(isLike){
            event.target.nextElementSibling.innerText = 'Dislike';
        } else{
            event.target.nextElementSibling.innerText = 'Like';
        }
    });
});

控制器:

public function postLikePost(Request $request){
    $post_id = $request['postId'];
    $is_like = $request['isLike'] === 'true';
    $update = false;
    $post = Post::find($post_id);
    if(!$post){
        return null;
    }
    $user = Auth::user();
    $like = $user->likes()->where('post_id', $post_id)->first();
    if($like){
        $already_like = $like->like;
        $update = true;
        if($already_like == $is_like){
            $like->delete();
            return null;
        }
    }else{
        $like->like = $is_like;
        $like->post_id = $post_id;
        $like->user_id = $user_id;
    }
    // This is working when the controller is updating but broken when saving
    if($update){
        $like->update();
    } else{
        $like->save();
    }
    return null;
}

p。S:
我是phpstorm和laravel的新手，如果你知道一个像eclipse那样调试/记录/观察变量值的好方法，我将不胜感激。