RegexStateMatcher includeNotifyingNodes(Collection<DummyVdsNode> nodes) {
            Objects.requireNonNull(nodes, "nodes must be non-null");
            nodesToCheck = nodes;
            return this;
        }
Return null if met, why not if it is not met.
clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/testutils/WaitCondition.java