better exception handling for API endpoint

[ratanparai]

I'm submitting a...

[x] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Other... Please describe:

Current behavior

Calling API endpoint return HTML page rather than json if something goes wrong in server side.

Expected behavior

API endpoint should always return result in json format. If there is any problem then it should return in json format too