filter doesn't change the type, it only removes elements

Removing all the null values would however effectively change the type from nullable String to string? So a smart cast seems sensible to me here?

Smart cast works on

it

inside the lambda

afaik not much you can do but to cast it 😞 but at least you can isolate that in a single place:

@Suppress("UNCHECKED_CAST")
fun <K, V> Map<K, V?>.filterNonNullValues() = filterValues { it != null } as Map<K, V>

That’s what I ended up doing @araqnid, thanks 🙂