tacker vnffg-create "Request Failed: internal server error while processing your request"

Hi,

I took the example of VNFFGD from https://github.com/openstack/tacker/tree/master/samples/tosca-templates/vnffgd. But when i initiate vnffg using 'tacker vnffg-create', I got the error message as "Request Failed: internal server error while processing your request".

$ tacker vnfd-list
+--------------------------------------+----------+-----------------+------------------------------+
| id | name | template_source | description |
+--------------------------------------+----------+-----------------+------------------------------+
| 60744e50-8b28-4467-a181-14f76e7f1d8e | VNFD1 | onboarded | Define VNF1 with 1 VDU an... |
| 9d55ab9b-328b-4118-8248-74702d99b3a6 | VNFD2 | onboarded | Define VNF2 with 1 VDU an... |
+--------------------------------------+----------+-----------------+------------------------------+

$ tacker vnf-list
+--------------------------------------+--------------------------+----------------------------+--------+----------------------------------
| id | name | mgmt_url | status | vim_id | vnfd_id |
+--------------------------------------+--------------------------+----------------------------+--------+----------------------------------
| 139592d9-2a68-4863-834a-ac71854feb82 | VNF2 | {"VDU1": "192.168.120.6"} | ACTIVE | 4e950da2-6ca9-4137-ba35-89237d779a6d | 9d55ab9b-328b-4118-8248-74702d99b3a6 |
| 17f04235-bcd1-4bb6-9014-539a7bd9a53c | VNF1 | {"VDU1": "192.168.120.3"} | ACTIVE | 4e950da2-6ca9-4137-ba35-89237d779a6d | 60744e50-8b28-4467-a181-14f76e7f1d8e |
+--------------------------------------+---------------------------+----------------------------+--------+----------------------------------

$ tacker vnffgd-list
+--------------------------------------+---------------+-------------+
| id | name | description |
+--------------------------------------+---------------+-------------+
| 8f1aba6d-2e55-45b5-910a-58219cfb6faa | sample-vnffgd | |
+--------------------------------------+---------------+-------------+

$ tacker vnffg-create --vnffgd-id 8f1aba6d-2e55-45b5-910a-58219cfb6faa --vnf-mapping VNF1:'17f04235-bcd1-4bb6-9014-539a7bd9a53c',VNF2:'139592d9-2a68-4863-834a-ac71854feb82' vnffg-vnf1-vnf2
Request Failed: internal server error while processing your request.

Please guide me how to solve this problem.