log exception on _create_connection failure
Merge branch 'informative-errors' of https://github.com/podshumok/cqlengine into podshumok-informative-errors
fixed issue with setting a list to an empty list
disallow saving None inside set and list
Fixed #90, putting None inside containers now throws a validation error
ensure we aren't trying to include polymorphic keys when we blah.objects.delete
version bump
fixed version