Not all 400 errors return a JSON response

[jackbentley]

It looks like some 4XX errors returned from Citadel sometimes don't contain a JSON response and have a blank response instead. I'm not sure what 4XX code this happens on but in the instance I found it's when we pass a token with the value undefined.

The code expects a JSON response with error details. However because there is none it throws a MalformedPayloadException which is confusing

citadel-php/src/Client.php

Lines 127 to 129 in 7eb2d66

	if ($statusCode >= 400) {
	ExceptionFactory::generateExceptionFromResponse($response);
	}