    @Test
    public void testNullValueChanged() throws Exception {

        try {
            Collection<DataTreeModification<Flow>> nullChanges = null;
            pathListener1.onDataTreeChanged(nullChanges);
            pathListener2.onDataTreeChanged(nullChanges);
        } catch (Exception e) {
            Assert.assertEquals(IllegalArgumentException.class, e.getClass());
        }

        Collection<DataTreeModification<Flow>> changes = new ArrayList<>();

        DataTreeModification<Flow> change0 = null;
        changes.add(change0);

        pathListener1.onDataTreeChanged(changes);
        pathListener2.onDataTreeChanged(changes);
    }