问c#中具有前缀读取问题的XML元素

EN

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:hdr="http://www.example.com/hdr/">
<soapenv:Header>
<hdr:ERROR_CODE>0</hdr:ERROR_CODE>
<hdr:ERROR_DESC>Success</hdr:ERROR_DESC>
<hdr:ASYNCH_RESPONSE_INDICATOR>0</hdr:ASYNCH_RESPONSE_INDICATOR>
</soapenv:Header>
<soapenv:Body><CREATE_RESPONSE></CREATE_RESPONSE>
</soapenv:Body>
</soapenv:Envelope>

var response = @"<soapenv:Envelope xmlns:soapenv='http://schemas.xmlsoap.org/soap/envelope/' xmlns:hdr='http://www.example.com/hdr/'>
                        <soapenv:Header>
<hdr:ERROR_CODE>0</hdr:ERROR_CODE>
<hdr:ERROR_DESC>Success</hdr:ERROR_DESC>
<hdr:ASYNCH_RESPONSE_INDICATOR>0</hdr:ASYNCH_RESPONSE_INDICATOR>
</soapenv:Header>
<soapenv:Body><CREATE_RETAILER_RESPONSE></CREATE_RETAILER_RESPONSE>
</soapenv:Body>
</soapenv:Envelope>";
        var responseXdoc = XDocument.Parse(response);
        var nsManager = new XmlNamespaceManager(new NameTable());
        nsManager.AddNamespace("hdr", "http://www.example.com/hdr");
        var statusElement = responseXdoc.XPathSelectElement("//hdr:ERROR_CODE", nsManager);
        
        Console.WriteLine(statusElement.Value);

[System.NullReferenceException: Object reference not set to an instance of an object.]
   at Program.Main() :line 26