VTN flowfilter delete fails when we delete entire configuration i.e., delete vtn of vtnflowfilter

In CSIT, faced issue while testing using the below scenario,
Used latest master branch from Git for testing.

Reproduce Scenario:
1) create vtn, vbr, interfaces, portmap, flowlist and flowlist entry, vtn flowfilter and vtn flowfilter entry.
2) Ping hosts.
3) Delete vtn – Here fails when we delete entire configuration of vtn flowfilter i.e., deleting vtn.

Note:
Only in vtnflowfilter the issue occurs, not in other flowfilter related keytypes.