Call to a member function save() on a non-object using ajax in laravel 5

<?php
    
    namespace App\Http\Controllers;
    
    use Illuminate\Http\Request;
    use App\Depress;
    use App\Http\Requests;
    
    class LikeController extends Controller
    {
        public function postLike(Request $request)
        {
            $post_id = $request->input('postId');
            //dd($post_id);
            $post = Depress::find($post_id);
            $post['like'] = $post['like'] + 1;
            $post->save();
            return null;
        }
    
        public function postDislike(Request $request)
        {
            $post_id = $request->input('postId');
            $post = Depress::find($post_id);
            $post['dislike'] = $post['dislike'] + 1;
            $post->save();
            return null;
        }
    }

$post->save();

<pre lang="PHP">