public static long findAndVerifyWindowGrace(final GraphNode graphNode) {
        return findAndVerifyWindowGrace(graphNode, "");
    }
@Test
    public void shouldThrowOnNull() {
        try {
            GraphGraceSearchUtil.findAndVerifyWindowGrace(null);
            fail("Should have thrown.");
        } catch (final TopologyException e) {
            assertThat(e.getMessage(), is("Invalid topology: Window close time is only defined for windowed computations. Got []."));
        }
    }