`traverse` requires applicative of some other kind...

# coroutines

[Egor Trutenko]

traverse requires applicative of some other kind, which a map is wrapped into, if I understand it correctly
So, this will work: mapK.traverse(Option.applicative()) { Some(it) }. It will wrap the map in Option, so it'll be Some(mapK)
Now, if mapK was listK, I would be able to call sequence on the result of traverse, feeding instance of ListK for `Applicative`:
Some(listOf(1, 2, 3)).sequence(ListK.applicative())
The same, unfortunately, doesn't work for MapK, for aforementioned problem of lacking applicative instance

[dave08]

The kdocs don't seem to correspond though:

public abstract fun invokeOnClose(
    handler: (Throwable?) → Unit
): Unit
Registers handler which is synchronously invoked once the channel is closed or receiving side of this channel is cancelled. Only one handler can be attached to the channel during channel's lifetime. Handler is invoked when isClosedForSend starts to return true. If channel is already closed, handler is invoked immediately.
The meaning of cause that is passed to the handler:
- null if channel was closed or cancelled without corresponding argument
- close or cancel cause otherwise.

The handler receives a Throwable?... not close or cancel?