I'm not suggesting we should. I'm suggesting we should only invoke the interactor if we have a category to give it.

For educational purposes we could make this less coupled by checking if the `category` quacks as required:

```rb
def initialize(category)
  raise(ArgumentError, "`category' must expose `parent_id`'") unless category.respond_to?(:parent_id)

  self.parent_id = category.parent_id
end
```