'WITH WITH' in alter keyspace statements causes NPE

Running any of these statements:

ALTER KEYSPACE WITH WITH DURABLE_WRITES = true;
ALTER KEYSPACE ks WITH WITH DURABLE_WRITES = true;
CREATE KEYSPACE WITH WITH DURABLE_WRITES = true;
CREATE KEYSPACE ks WITH WITH DURABLE_WRITES = true;

Fails, raising a SyntaxException and giving a NullPointerException as the reason for failure. This happens in all versions I tried, including 2.0.15, 2.1.5, and HEAD on cassandra-2.0, cassandra-2.1, cassandra-2.2, and trunk.

EDIT: A dtest is here, but it would probably be more appropriate to test with unit tests.