Unable to create mirror on WASB target due to "Cluster entity not found"

1. Create a mirror which source cluster is the one created , and dummy target cluster
2. Save

Submitting the mirror from CLI （see log below）:
1) with WASB url on "targetCluster", it complained that the WASB was invalid
or
2) with nothing on "targetCluster", it complained that "Cluster entity not found"

1. cat /tmp/hdfsMirroring.props
   jobName=testjob
   jobClusterName=primaryCluster
   jobValidityStart=2017-01-13T00:00Z
   jobValidityEnd=2017-12-30T00:00Z
   jobFrequency=minutes(5)
   sourceDir=/data/testdir
   sourceCluster=primaryCluster
   targetDir=/data/testdir
   targetCluster=

1. su - falcon
2. /usr/hdp/current/falcon-server/bin/falcon extension -submit -extensionName hdfs-mirroring -file /tmp/hdfsMirroring.props
   ERROR: Internal Server Error;Cluster entity not found