Always return JSON responses
When a GraphQL resolver that is hooked up to a REST endpoint returns null, graphql2rest returns a response with no body, and no Content-Type header.
The expected behavior in my opinion would be that the REST endpoint returns a JSON response containing the JSON null. By specifying res.json instead of res.send, the response will always contain a valid JSON response.
@thecodeboss: after your change, what does graphql2rest return when the manifest defines a 204 No Content success status code (for, say, a DELETE operation)?
GraphQL will of course always return a JSON response, but even an empty JSON may be seen as violating the "No Content" standard for 204 HTTP code.
Since an empty JSON object may be seen as violating the "No Content" standard for 204 HTTP code, we should not ALWAYS return JSON responses. Therefore closing this PR without merging.