Error 500 with save() method of eloquent/laravel

I want to save an object with eloquent/laravel but i get error 500 there is my model code :

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Categorie extends Model
{

}

action :

public function addCategorie() {
        $input = Input::all();
        $categorie = new Categorie;
        $categorie->libelle = $input['label'];
        $categorie->save();
        return $categorie;
    }

when i get the print_r($categorie) after the save method i get a result , when i use the save methode i got an error 500

via Chebli Mohamed