@Override
    public void validate(ChangeContext context) {
            for (Map.Entry<String, ContentCluster> currentEntry : context.previousModel().getContentClusters().entrySet()) {
                ContentCluster nextCluster = context.model().getContentClusters().get(currentEntry.getKey());
                if (nextCluster == null) continue;

                validateContentCluster(context, currentEntry.getValue(), nextCluster);
            }
    }
Class that adds a validation failure if global attribute changes for a document
type in a content cluster unless corresponding override is present.
config-model/src/main/java/com/yahoo/vespa/model/application/validation/change/GlobalDocumentChangeValidator.java