allow null as Entry/Map item
fix up issue with defines() for Maps with null items
entries can now have null items
update doc for Entry.equals()
update doc for Entry.string
Revert "fix type expression"

This reverts commit 565f47cfd56f5a57650d21ae078e2e64f34785d8.
Revert "fix for fix for fix for #554"

This reverts commit 31204ff959f61242c94f481ef438ae2fc2fa22c8.
rollback some changes that are not needed on this branch
fix test
fix test after changes to Iterable.indexed
optimize List.contains()