Removing Element from XML in C#

below is the xml and i need to remove the Element SMS where code equals to "ZOOMLA". i am using C# code as below but it does not work. and gives me "object reference error"

 XDocument doc = XDocument.Parse(xml);
XElement sms = (from xml2 in doc.Descendants("SMSList").Descendants("SMS")
                                where xml2.Attribute("Code").Value == code
                                select xml2).FirstOrDefault();
sms.Remove();

---

 <?xml version="1.0" encoding="utf-16" ?> 
- <Parent>
  <ServiceList /> 
 <VoiceList /> 
- <SMSList>
- <SMS>
 <Code>ZOOMLA</Code> 
 <Name>Zoom Limited</Name> 
 <SubType>Prepaid</SubType> 
 - <Fields>
 - <Field>
 <ID>222</ID> 
 <Name>Charges</Name> 
 <CValue>1</CValue> 
 <Priority>0</Priority> 
</Field>
</Fields>
</SMS>
</SMSList>
<DataList /> 
<LBCOffer /> 
</Parent>