Handle unexpected 204 errors?

[jwietelmann]

When using the address validation endpoint, I momentarily forgot to have my test POST any params. Instead of receiving any kind of error, I got a 204 No Content, which implies success. (This is something I'd consider a bug on TaxJar's end, but it would demand an API version bump if fixed, IMO.)

Anyway, my code's returning {:ok, _} in this case. But it's not okay! What actually happened was the API server more or less rejected the request for lack of appropriate params.

(Cursory testing suggests the problem is probably limited to /addresses/validate.)