Input send NULL array on laravel 5.3

i have this error when I try to send an array to my database table. i have this on my update method

$post = Post::findOrFail($id);
        $post->PostTitle = $request->PostTitle;
        $post->post = $request->post;
$tags = new Tag;
         foreach ($request->tags as $tags) {
           $tag = Tag::create(['tag'=>$tags]);
           if($tag->save()){
             $post->tags()->sync($tag->id);
           }
         }

this is my html form

<div class="post-panel-3">
        <div class="form-group">
          <label for="postTags">Etiquetas: </label>
            <input type="text" name="taggged[]" class="form-control" placeholder="Etiquetas" value="<?php if(isset($post->tags)){ foreach($post->tags as $tag); echo $tag->tag;} ?>" id="tagBox2">

I have ManyToMany relationship model, all run fine in create method but no on update. I think i miss something but not finded yet.

via Johanng1993