@Override
    public void startStream() {
        try {
            if (idEnrichmentExpectedIds.getStreamId() == null) {
                final Meta meta = metaHolder.getMeta();
                if (meta != null) {
                    idEnrichmentExpectedIds.setStreamId(meta.getId());
                } else {
                    final String msg = "No stream set in stream holder";
                    errorReceiverProxy
                            .log(Severity.WARNING, null, getElementId(), msg, ProcessException.create(msg));
                }
            }
            depth = 0;
        } finally {
            super.startStream();
        }
    }
This method tells filters that a stream is about to be parsed so that
they can complete any setup necessary.
stroom-pipeline/src/main/java/stroom/pipeline/filter/IdEnrichmentFilter.java