Fixed NullPointerException occuring when LockFeature (WFS) is requested via SOAP

[dstenger]

When a WFS is used to request LockFeature via SOAP, a NPE occurs:

<ows:ExceptionReport xsi:schemaLocation="http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsExceptionReport.xsd" version="2.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <ows:Exception exceptionCode="InvalidRequest">
      <ows:ExceptionText>java.lang.NullPointerException</ows:ExceptionText>
   </ows:Exception>
</ows:ExceptionReport>

This pull request fixes this so that a valid response is returned (equal to the one retrieved by POST).