test to show blind update of empty map causes AttributeError
test to show blind update of empty set causes CQLEngineException
Merge branch 'master' into update-with-empty-map
Can blind update a map column such that it becomes an empty map.
Can blind update a set column such that it becomes an empty set.
test for blind update of empty list
slight change to way blind update to empty handled in MapUpdateClause
fixing get_context_size for blind update to None in SetUpdateClause
slight fix to MapUpdateClause context size.  Fix MapUpdateClause assignment clause test.
Merge branch 'update-with-empty-map' of github.com:Lifto/cqlengine into Lifto-update-with-empty-map