How to use XPATH functions in Mule

I have an input SOAP XML as follows :-

<soapenv:Envelope xmlns:soapenv="http://ift.tt/sVJIaE" xmlns:v1="http://ift.tt/1kFt6Sx">
   <soapenv:Header>
    </soapenv:Header>
   <soapenv:Body>
      <v1:retrieveDataRequest>
         <v1:Id>662</v1:Id>
      </v1:retrieveDataRequest>
   </soapenv:Body>
</soapenv:Envelope>

Now my question is simple ...

How can I use XPATH functions like count(),name(),substring() etc in Mule

I want to use XPATH on this SOAP request like the following :-

 <logger message="#[xpath('count(//v1:retrieveDataRequest/v1:Id)')]" level="INFO" doc:name="Logger"/>

But It is throwing following exception :-

java.lang.RuntimeException: org.mule.api.MuleRuntimeException: Failed to evaluate XPath expression: "count(//v1:retrieveDataRequest/v1:Id)"
    at org.mule.module.xml.el.XPathFunction.call(XPathFunction.java:70)

Please note :- I have already used Mule namespace-manager as following :-

<mulexml:namespace-manager includeConfigNamespaces="true">
    <mulexml:namespace prefix="soapenv" uri="http://ift.tt/sVJIaE"/>
    <mulexml:namespace prefix="v1" uri="http://ift.tt/1kFt6Sx"/>
</mulexml:namespace-manager>

and I am getting results for the following :- <logger message="#[xpath('//v1:retrieveDataRequest/v1:Id').text]" level="INFO" doc:name="Logger"/>

Please help