I have legacy code using a map of maps.

In the last level the values are lists (as opposed to maps),
and not all the levels have the same key type.

I've tried defining a

Map<?, ?>

for this (is there a better solution?)
but when I try to insert an entry to the map I get the following error:

The method put(capture-of ?, capture-of ?) in the type Map is not
applicable for the arguments ...

Any suggestions?