@Override
    public void endPrefixMapping(final String prefix) throws SAXException {
        if (depth > 1) {
            super.endPrefixMapping(prefix);
        }
    }
Don't end prefix mappings if we are at the root element. Leave the end
processing method to do this.
stroom-pipeline/src/main/java/stroom/pipeline/filter/MergeFilter.java