public static ObjectNode generateAnnotObjectNode(ChartModel cm) {
        ObjectNode node = MAPPER.createObjectNode();
        for (ChartModel.Annot a : cm.getAnnotations()) {
            node.put(a.key(), a.valueAsString());
        }
        return node;
    }
@Test
    public void annot() {
        ChartModel cm = new ChartModel(FOO, BAR);
        cm.addAnnotation("dev1", "of:0000000000000001");
        cm.addAnnotation("dev2", "of:0000000000000002");

        ObjectNode node = ChartUtils.generateAnnotObjectNode(cm);
        Assert.assertEquals("wrong results", NODE_AS_STRING, node.toString());
    }