Allow skipping the type gets on getSet/getList/getMap

I have some reflection tools wired up to bind Rows to objects, and it's a little bit of a pain to know the Class instances of the generics on the bound Maps. This patch is a little on the hacky side, but I added the option that if you explicitly pass in null values for the elements classes, it allows you to bypass the checks. I wouldn't mind making explicit getUncheckedSet / getUncheckedList / etc methods, though, if you're agreeable to the idea but offended by the simpler implementation. I was just trying to avoid introducing new API for what might be an edgey case.