Laravel 关系方法必须返回 Relation 类型的对象

我一直在谷歌上搜索，试图找出一个解决方案。我得到：

ErrorException in Model.php line 2755: Relationship method must return an object of type Illuminate'Database'Eloquent'Relations'Relation

当我尝试转到我的帖子索引页面时出错，并且无法弄清楚它来自哪里。当我从创建帖子重定向时，我可以进入该页面，但之后我收到错误。据说它应该来自不返回关系，但这是我的关系和代码：

发布

public function category() 
{
    return $this->belongsTo('App'Category', 'category_id');
}
public function user()
{
    return $this->belongsTo('App'User', 'user_id');
}

用户

public function roles() 
{
    return $this->belongsToMany('App'Role')->withTimestamps();
}
public function posts()
{
    return $this->hasMany('App'Post', 'user_id');
}

角色

 public function users() 
{
    return $this->belongsToMany('App'User');
}

类别

public function posts()
{
    return $this->hasMany('App'Post', 'category_id');
}

索引刀片.php

@extends('app')
@section('content')
	<h1>Posts</h1>
	@if (Auth::check()) 
		@if (Auth::user()->isAdmin())
			<a href="/post/create">Create a Post</a>
		@endif
	@endif
	@foreach ($posts as $post)
		@include('includes.post', ['post' => $post, 'link' => true])
	@endforeach
@stop

和后刀片.php

<div class="post">
	<div class="div">
		<div class="postCategory">
		
		</div>
		@if($link)
			<a href="/post/{{ $post->id }}"><h2>{{ $post->title }}</h2></a>
		@else
			<h2>{{ $post->title }}</h2>
		@endif
		<p>{!! $post->body !!}</p>
		<p>{{ $post->category->name }}</p>
		<p>Posted by <a href="/user/{{ $post->user->username }}">{{ $post->user->username }}</a> at {{ $post->created_at }}</p>
		
		@if(Auth::check())
			@if($post->user->username == Auth::user()->username || Auth::user()->isAdmin)
				{!! Form::open(['method' => 'delete', 'route' => ['post.destroy', $post->id]]) !!}
					<input type="submit" value="Delete Post" onclick="return confirm('Are you sure?')"></input>
				{!! Form::close() !!}
			@endif
		@endif
		
	</div>
</div>