How to use morphMany with a custom function in a model

(This is about Laravel 5.8)

I know you can create custom functions in your model, but I can't figure out how to make a custom function that uses data from the function morphMany.

What works:
model.php:

public function images()
{
    return $this->morphMany('App\Image', 'owner');
}

page.blade.php:

@foreach($model->images() as $image)
    
@endforeach

This works. But I want to create a function that for example only gives the poster back. But when I place that foreach in a function inside my model. It won't loop trough the images. See the following code:

What doesn't work:
model.php:

public function images()
{
    return $this->morphMany('App\Image', 'owner');
}

public function poster()
{
    $images = $this->morphMany('App\Image', 'owner');

    foreach($images as $image)
        /* THIS CODE WILL NEVER RUN SOMEHOW */
        if ($image->type == "poster")
        {
            return $image;
        }
    }
    return NULL;
}

The code just returns NULL, what am I missing?

via Chebli Mohamed