public void checkUniqueId(final NodeFactory nodeFactory) {
        final String id = nodeFactory.getId();
        if (id != null) {
            if (!uniqueIdSet.add(id)) {
                throw new RuntimeException("Duplicate id: " + id);
            }
        }
    }
Checks node id to ensure uniqueness.
stroom-pipeline/src/main/java/stroom/pipeline/xml/converter/ds3/ref/VarFactoryMap.java