Sorting is not working for edge_vertex query with embedded_dj repo

Edge-vertex query with sorting is not working for embedded_dj repo.

Steps to reproduce:

1. deploy IDM with sample sync-with-csv
2. execute reconcialiation
3. run this query

   curl -X GET \
     'http://idm.example.com:8080/openidm/internal/role/openidm-authorized/authzMembers?_queryFilter=_refResourceCollection%20eq%20%27managed/user%27&_sortKeys=userName' \
     -H 'Content-Type: application/json' \
     -H 'Cookie: session-jwt=' \
     -H 'X-OpenIDM-Password: openidm-admin' \
     -H 'X-OpenIDM-Username: openidm-admin' \
     -H 'cache-control: no-cache'
   

4. Then execute another query with reverse sorting:

   curl -X GET \
     'http://idm.example.com:8080/openidm/internal/role/openidm-authorized/authzMembers?_queryFilter=_refResourceCollection%20eq%20%27managed/user%27&_sortKeys=-userName' \
     -H 'Content-Type: application/json' \
     -H 'Cookie: session-jwt=' \
     -H 'X-OpenIDM-Password: openidm-admin' \
     -H 'X-OpenIDM-Username: openidm-admin' \
     -H 'cache-control: no-cache'
   

Expected results: records should be sorted accordingly
Actual results: record are not sorted correctly, the results is same for both queries