Balance optional on some accounts.

Author: tjlytle

src/Nexmo/Message/Response/Message.php

@@ -21,13 +21,12 @@ public function __construct(Array $data, Receipt $receipt = null)
             'status',
             'message-id',
             'to',
-            'remaining-balance',
             'message-price',
             'network'
         );
 
         //default value
-        $data = array_merge(array('client-ref' => null), $data);
+        $data = array_merge(array('client-ref' => null, 'remaining-balance' => null), $data);
 
         $return = parent::__construct($data);