private static String createDotString(Map<String, NameProvider> cycleNodes) {
        StringBuilder res = new StringBuilder();
        res.append("digraph dependencyGraph {\n");

        Set<Node> used = new HashSet<>();
        for (Node node: cycleNodes.values()) {
            if (!node.ready())
                node.dotDependenciesString(res, used);

        }
        res.append("}");
        return res.toString();
    }
Signals that the dependency graph contains cycles. A DOT language
representation of the cycle is available to help solve the problem (<a
href="http://graphviz.org/">GraphViz</a>).

@author Tony Vaagenes
container-core/src/main/java/com/yahoo/component/chain/dependencies/ordering/CycleDependenciesException.java