Checking the presence of category isn't assisting you with that. It's protecting against you invoking `CategoryParentsReader` with a `nil` category. You should do this like so:

```rb
def initialize(category)
  raise(ArgumentError, "`category' must be a `Core::Category'") unless category.is_a?(Core::Category)
  
  self.parent_id = category.parent_id
end
```

**BUT** - do we want type checking, or do we need to ensure we're invoking the interactor correctly elsewhere?