That means you don't have a clean "domain model" (or business logic layer) and a data filtering layer that creates the domain objects. You should apply business logic on the pure objects/entities, and you should make sure that the filtering handles the representational problems (parsing, data integrity, partial data, and so on).

And ideally if something makes it through the data filtering layer into the logic layer and does not make sense there, then that should be handled. And that's where strong types help. It forces you to handle these cases, even if that means logging/alerting/ignoring, but at least you'll have to make a decision when you write the logic, instead of 3AM in the morning.