Fix a bug that happened when you uploaded an empty file.

application/modules/requests/models/RequestModel.php

@@ -707,7 +707,7 @@ class Requests_RequestModel extends Unl_Model
     public function __sleep()
     {
     	foreach ($this->_data['files'] as &$file) {
-    		if (!$file['data']) {
+    		if (array_key_exists('hash', $file) && !$file['data']) {
     			continue;
     		}
     		$file['hash'] = self::_saveFileToDisk($file['data']);