Watching a reposoitory from REST API isn't reflected in 'Watched repositories'

Issue Summary

Whenever a user watches a fresh repository using the following API. The 'watch' in UI changes to 'watching'. However the repository is not shown under the 'watched repositories' also no email notifications are sent 

Steps to Reproduce

1. Watch the repo using the following API

   curl -u username -X POST -H "Content-Type: application/json" -d '{}' 'http://localhost:7991/rest/api/1.0/projects/TEST/repos/demo3/watch'
   

1. Step 2
   Look for the repository in watched repositories. 

Expected Results

The repository should be visible in 'watched repositories'

Actual Results

The repository isn't visible in 'watched repositories'
The below exception is thrown in the xxxxxxx.log file:

...

Workaround

No workaround available at the moment