@Override
    public void endProcessing() {
        super.endProcessing();
    }
Used to determine whether any events have been passed on to the child
filter. If none have been passed on when this filter received an end
document event then the start and end document events shall be passed to
the child filter to ensure the rest of the pipeline does some processing.
stroom-pipeline/src/main/java/stroom/pipeline/filter/SplitFilter.java