[axis2] Why findNamespace returns null when called on SOAP header ?

[Gul Onural]

I am trying to extract data from SOAP message header, using axis2 raw
xml message receivers.
My SOAP envelope look like :

<?xml version='1.0' encoding='utf-8'?>
<soapenv:Envelope
xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/";>
    <soapenv:Header>
          <tns:UserId
xmlns:tns="http://www.mycompany.com/MyService";>someUser</tns:UserId>
    </soapenv:Header>
    <soapenv:Body />
</soapenv:Envelope>

Using the following code I am getting ns always null. What would be
missing in this code ? 

Gul

import org.apache.axiom.soap.SOAPHeader;
import org.apache.axiom.soap.SOAPEnvelope;

    public OMElement getXXX(OMElement inputMsg) throws AxisFault {
        // This message doesn't have body. Get namespace prefix from the
SOAP header
        // Do I need inputMsg as in parameter here ?
        MessageContext msgContext =
MessageContext.getCurrentMessageContext();
        String nsPrefix = null;
        SOAPEnvelope envelope = msgContext.getEnvelope();
        // Envelope looks good...
        if (envelope != null) {
            SOAPHeader header = envelope.getHeader();
            if (header != null) {
                // Header is good
                OMNamespace ns = header.findNamespace(
                        "http://www.mycompany.com/MyService";, null);
                if (ns != null) {
                    // ns is ALWAYS null..Why ?
                    nsPrefix = ns.getPrefix();
                    if (nsPrefix != null) {
                        ...
                    }
                }
            }
        }
...
}