Fix returning null from endpoints

[utkarshkukreti]

#1808 introduced a bug which converts null to {} (empty object) when returned from endpoints. This PR fixes it and includes a test for the fix.

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[utkarshkukreti]

I used typeof body === 'undefined' because the code above used it, but I think body === undefined would have identical behavior here? Any reason to prefer the former?

[ignatiusmb]

Good catch! Would it make sense to check for other types as well outside of "object"?

Any reason to prefer the former?

typeof is safer and used it out of habit, but since we know body is already defined, we can probably omit it.