4.1 added the ability for LWT to support "UPDATE ... SET name = name + 42", but we never really fleshed out with the larger community what the semantics should be in the case where the column or row are NULL; I opened up https://issues.apache.org/jira/browse/CASSANDRA-17857 for this issue.
As I see it there are 3 possible outcomes: 1) fail the query 2) null + 42 = null (matches SQL) 3) null + 42 == 0 + 42 = 42 (matches counters) In SQL you get NULL (option 2), but CQL counters treat NULL as 0 (option 3) meaning we already do not match SQL (though counters are not a standard SQL type so might not be applicable). Personally I lean towards option 3 as the "zero" for addition and subtraction is 0 (1 for multiplication and division). So looking for feedback so we can update in CASSANDRA-17857 before 4.1 release.
