@Override
    public void startPrefixMapping(final String prefix, final String uri) throws SAXException {
        handler.startPrefixMapping(prefix, uri);
        super.startPrefixMapping(prefix, uri);
    }
@param prefix the Namespace prefix being declared. An empty string is used
              for the default element namespace, which has no prefix.
@param uri    the Namespace URI the prefix is mapped to
@throws SAXException the client may throw an exception during processing
@see #endPrefixMapping
@see #startElement
@see AbstractXMLFilter#startPrefixMapping(String,
String)
stroom-pipeline/src/main/java/stroom/pipeline/filter/AbstractSamplingFilter.java