Yep! On of the things I point out most frequently in code reviews are things like this. However, null is an imperfect system for capturing such state. It's not self-documenting, and it breaks down when you have more than 2 states to represent.

Languages with Sum Types represent this much more elegantly with arbitrary numbers of variants and force you to check which one you have before accessing the more specific data (e.g. the filter) inside.