Minor Description
A coworker of mine just had this scenario. It does not make sense the EMPTY_START_ROW as splitKey (since the region with the empty start key is implicit), but it should not cause the HMaster to abort.
The abort happens because it tries to bulk assign the same region twice and then runs into race conditions with ZK.
The same would (presumably) happen when two identical split keys are passed, but the client blocks that. The simplest solution here is to also block passed null or EMPTY_START_ROW as split key by the client.