private boolean writeFieldName() throws IOException {
        if (currentDocFieldName != null) {
            jsonGenerator.writeFieldName(currentDocFieldName);
            return true;
        } else {
            return false;
        }
    }
@param ch     the characters from the XML document
@param start  the start position in the array
@param length the number of characters to read from the array
@throws org.xml.sax.SAXException any SAX exception, possibly wrapping another exception
@see #ignorableWhitespace
@see org.xml.sax.Locator
@see stroom.pipeline.filter.AbstractXMLFilter#characters(char[],
int, int)
stroom-search/stroom-search-elastic/src/main/java/stroom/search/elastic/indexing/ElasticIndexingFilter.java