One company (who I will refer to as Company NNN from here forth), has a REST API. At my company, we use Company NNN's REST API to provide some content to our end users.
If I send the request with the User-Agent header field filled in, the REST API returns valid JSON data. If I send the request without the User-Agent header field filled in, the REST API returns 500 Internal Server Error. Upon notifying Company NNN of this, their response to me was that specifying a User-Agent is best practice.
Shouldn't this API be able to return valid JSON even without a User-Agent request header?