Laravel - Relationships - Morph One To One Key Conventions

If necessary, you may specify the name of the "id" and "type" columns utilized by your polymorphic child model. If you do so, ensure that you always pass the name of the relationship as the first argument to the morphTo method. Typically, this value should match the method name, so you may use PHP's __FUNCTION__ constant:

     * Get the model that the image belongs to.
    public function imageable()
        return $this->morphTo(__FUNCTION__, 'imageable_type', 'imageable_id');