using item() breaks if relationship doesnt exist collection() doesnt break?

so if in my transformer i do something like

```
public function includeTestimonials(Entity $item)
{
return $this->collection($item->testimonials, new TestimonialTransformer, true);
}
```
this works even if testimonials is missing

but

```
public function includeShop(Entity $item)
{
if ( $item->shop )
return $this->item($item->shop, new ShopTransformer, true);
}
```

i have to add in an if check otherwise this gives me an error shop entity expected null given? i dont want to be adding lots of if statements..