apollo-datasource-rest RESTDataSource does not handle HTTP 204 responses correctly

[dhm116]

We noticed that the RESTDataSource.parseBody method was not handling HTTP 204 responses correctly in the event that a Content-Type: application/json header was being defined on the response.

This PR resolves that issue by inspecting the response.status to ensure that it is not 204 before attempting to process the response as JSON.

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[apollo-cla]

@dhm116: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[jplock]

We ran into this issue with an API behind AWS API Gateway where we were returning a 204 status code with no Content-Type response header. API Gateway seems to be adding a Content-Type: application/json response header if one isn't defined and we haven't yet figured out a way to disable that. To @dhm116's point, the Content-Length header value is properly being set to zero.

[dhm116]

I'll get the tests fixed up today!

[bartverbruggen]

This is fixed in #2446