cbbackup crashes when there are Search index aliases

$ /opt/couchbase/bin/cbbackup http://127.0.0.1:8091 ./backup -u Administrator -p password

  [                    ] 0.0% (0/estimated 7303 msgs)

bucket: beer-sample, msgs transferred...                           

       :                total |       last |    per sec            

 byte  :                    0 |          0 |        0.0            

Traceback (most recent call last):                                           

  File "/opt/couchbase/lib/python/cbbackup", line 12, in <module>             

    pump_transfer.exit_handler(pump_transfer.Backup().main(sys.argv))

  File "/opt/couchbase/lib/python/pump_transfer.py", line 80, in main

    rv = pumpStation.run()

  File "/opt/couchbase/lib/python/pump.py", line 148, in run

    rv = self.transfer_bucket_fts_index(source_bucket, source_map, sink_map)   

  File "/opt/couchbase/lib/python/pump.py", line 291, in transfer_bucket_fts_index

    source_bucket, source_map)                                                 

  File "/opt/couchbase/lib/python/pump_dcp.py", line 142, in provide_fts_index

    result, errors = rest.get_fts_index_metadata(source_bucket['name'])

  File "/opt/couchbase/lib/python/cluster_manager.py", line 147, in get_fts_index_metadata

    sourceName = index_def["sourceName"]                                     

KeyError: 'sourceName'