datastax/java-driver — pull request #225 by rstrickland (2014-09-13 19:07:37+00:00)
Title: (JAVA-451) DCAwareRoundRobinPolicy needs to throw an exception when explicitly specified DC is null or empty

The default is to use the first host to figure out the data center when it isn't specified. But if the user is calling the explicit constructor, it should throw an exception when this value is null or empty.