@Test
    public void shouldThrowIfValueIsNull() {
        try {
            GraphVariableHelper.validateVariable("test", null);
            fail("Should have thrown an exception when value is null");
        } catch (Exception iae) {
            final Exception expected = Graph.Variables.Exceptions.variableValueCanNotBeNull();
            assertEquals(expected.getClass(), iae.getClass());
            assertEquals(expected.getMessage(), iae.getMessage());
        }
    }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/structure/util/GraphVariableHelperTest.java