Merge pull request #13 from aubryfr/hotfix/verify_AttachableResponse_…

…structure

Verying the QuickBooks Attachable response against the expected structure

src/DataService.php

@@ -296,8 +296,16 @@ public function upload($fileName, $contentType, $content)
         ];
         $response = $this->request('POST', $this->getRequestUrl('upload'), $body, $headers);
 
+        if (!isset($response['AttachableResponse'])) {
+            throw new \UnexpectedValueException('The QuickBooks response should contain an "AttachableResponse" node');
+        }
+
         $response = reset($response['AttachableResponse']);
 
+        if (false === $response) {
+            throw new \UnexpectedValueException('The QuickBooks AttachableResponse is empty');
+        }
+
         if (isset($response['Fault'])) {
             throw $this->createFaultException($response);
         }