@Override
    public void setDocumentLocator(final Locator locator) {
        if (handler != null) {
            handler.setDocumentLocator(locator);
        } else {
            super.setDocumentLocator(locator);
        }
    }
Buffers a setDocumentLocator event if buffer is set to true.

@param locator an object that can return the location of any SAX document
               event
@see stroom.pipeline.filter.AbstractXMLFilter#setDocumentLocator(org.xml.sax.Locator)
stroom-pipeline/src/main/java/stroom/pipeline/filter/BufferFilter.java