in lib/aws/session_store/dynamo_db/locking/base.rb [73:79]
def save_exists_opts(env, sid, session, options = {})
add_attr = options[:add_attrs] || {}
expected = options[:expect_attr] || {}
attribute_opts = merge_all(attr_updts(env, session, add_attr), expected)
merge_all(table_opts(sid), attribute_opts)
end