fix: Ensure that falsy response bodies are correctly handled

[jaridmargolin]

Description

The title should be fairly descriptive of what is implemented. Before the PR, if a recorded request returned a body with the value of false or null, on subsequent usage, it would incorrectly be loaded as an empty string. This small patch ensures the value is accurately replayed.

Note: This was opened up against main because no next or beta branches were found.

[mastermatt]

Returning an empty string is intended behavior. The native http module in Node, which Nock makes a point to mimic as close as possible, will always return a buffer. Never null or undefined. And if the buffer can be stringified by the client, that is intended/expected.

[jaridmargolin]

@mastermatt There may be a misunderstanding due to my description. I have a concrete bug where nock is incorrectly changing a JSON response, where the value of that JSON is false, to an empty string when loading and replaying.

I may have oversimplified the solution due to my lack of knowledge of the internals, but with the above patch, all tests are still passing and the failing case is fixed.

[mikicho]

@jaridmargolin IIUC and according to the types, responses must be either a string or an object. Maybe the problem is in the recorder, which saves value as a boolean?