Resource Controller methods with model as parameter not working

As in the basic Laracasts.com tutorial (Laracast 5.7 from scratch) I'm trying to use the following methods public function show(prototypes $prototypes) parameter to construct a view. However my view is created correctly but $prototypes is null.

The route works well(/prototypes/1/edit) and I ensured that a prototype object with the id 1 exists. I found some older solution which stated to use something like (integer $id) as parameter but this leads to some more code. It should work like this:

Controller:

public function edit(prototypes $prototypes)
    {
        //
        return view('prototypes.edit', compact('prototypes'));
    }

According to Laracast From Scratch this should work.

Do you know how I could fix this?

What mechanism is behind this that the prototypes.edit method knows how to use the correct parameter?

via Chebli Mohamed