private void fastInfoSetStartDocumentIfNeeded() throws SAXException {
        if (!isFastInfosetDocStarted) {
            LOGGER.trace("saxDocumentSerializer - startDocument()");
            saxDocumentSerializer.reset();
            stagingValueOutputStream.reset();
            appliedPrefixToUriMap.clear();
            saxDocumentSerializer.startDocument();
            isFastInfosetDocStarted = true;
        }
    }
@param ch     An array of characters.
@param start  The starting position in the array.
@param length The number of characters to use from the array.
@throws SAXException The client may throw an exception during processing.
@see stroom.pipeline.filter.AbstractXMLFilter#characters(char[],
int, int)
stroom-state/stroom-state-impl/src/main/java/stroom/state/impl/pipeline/StateFilter.java