From reading the code in [KeysCommand](https://github.com/twitter/finagle/blob/master/finagle-redis/src/main/scala/com/twitter/finagle/redis/protocol/commands/CommandTypes.scala#L20), it looked like empty key values would throw an exception as well. My [unit test](https://github.com/jbripley/finagle/blob/add-redis-sinter-command/finagle-redis/src/test/scala/com/twitter/finagle/redis/integration/ClientSpec.scala#L257) seems to indicate that this is true as well.

I can remove that part of the comment though, if you think it'll only confuse people.