Unable to Handle Empty API Error Responses #4356

A smoke test request was made using the \Alphagov\Notifications\Client::sendSms method.

An error was thrown Warning: Trying to access array offset on null which came from Alphagov\Notifications\Exception\ApiException::__construct at line 19.

From what I can see the APIException is always expecting the body to be defined & have an error key. In this case the stream returned null and led to the error above.