Form validation in model

I am following the News tutorial and now I try to move the validation from the News controller/create() to the  News model. 
Controller: 

PHP Code:

<?php namespace App\Controllers;
use App\Models\NewsModel;
use CodeIgniter\Controller;

class News extends Controller
{    
    public function create()
    {
        helper('form');
        $model = new NewsModel();

        if ($model->save([
                'title' => $this->request->getVar('title'),
                'slug'  => url_title($this->request->getVar('title')),
                'body'  => $this->request->getVar('body'),
            ]) === false)
        {
            echo view('templates/header', ['title' => 'Create a news item']);
            echo view('news/create', ['errors' => $model->errors()]);
            echo view('templates/footer');
        }
        else
        {
            echo view('news/success');
        }
    }
} 


News Model:

PHP Code:

<?php namespace App\Models;

use CodeIgniter\Model; // Loads database library etc

class NewsModel extends Model
{
    protected $table = 'news'; 
    protected $returnType = 'object';
    protected $allowedFields = ['title', 'slug', 'body'];

    protected $validationRules    = [
        'title' => 'required|min_length[3]|max_length[255]',
        'body'  => 'required'
    ];

    protected $validationMessages = [
        'body'        => [
            'required' => 'Can not be empty!'
        ]
    ];
    
} 


I expected the validation rules stated in $validaiotnRules to kick in on $model->save().
The actual result is that I get the "Whoops" error when calling News/create()