BrokenDependency breakage = failuresByRevisionId.get(selector);
        if (breakage == null) {
            breakage = new BrokenDependency(failure);
            failuresByRevisionId.put(selector, breakage);
        }
        breakage.requiredBy.add(dependency.getFrom());
    }

    private static class BrokenDependency {
        final ModuleVersionResolveException failure;