Why ORM doen't send me back the Object?

I am working on Laravel 5.4 and i have a question about ORM. Why the behaviour of this two samples of codes send differents informations :

Foo::whereId(13632)->first(); => null

DB::table('foo')->where('id', '=', 13632)->first(); => Foo{...}

My class Foo :

class Foo extends Model
{
       protected $table = 'foo';

 ...
}

If i try do to this in my db (SQL) :

SELECT * FROM `doctors` WHERE `id` = 13632

I got the line with all the datas.

Thank you.

via Chebli Mohamed