401 Unauthorized error on querying for nullable field using synthetic graphql

Question

I'm using synthetic graphql feature of Azure to call an azure function. This Azure function is calling a remote end point and post processing its response before returning to gateway.

While graphql resolver is working like charm in returning only those attributes Im asking for in query, it fails when I pick a nullable attribute with 401 error.

I have attached trace for both working and failing scenarios with this post.

Is there any way we notify schema of attributes that are nullable or am I missing something here.success_failure_response.log