private boolean writeKey() {
        if (currentKey == null) {
            return false;
        }

        try {
            jsonGenerator.writeFieldName(currentKey);
        } catch (final IOException e) {
            fatal(e);
        }

        currentKey = null;
        return true;
    }
@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-pipeline/src/main/java/stroom/pipeline/writer/JSONWriter.java