The "NULL" operator in Expected (old-style conditional operations) doesn't have any parameters, so we insisted that the AttributeValueList be empty. However, we forgot to allow it to also be missing - a possibility which DynamoDB allows. This patch adds a test to reproduce this case (the test passes on DyanmoDB, fails on Alternator before this patch, and succeeds after this patch), and a fix. Fixes #6816. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20200709161254.618755-1-nyh@scylladb.com>