@Test
    @FeatureRequirement(featureClass = Graph.Features.GraphFeatures.class, feature = FEATURE_TRANSACTIONS)
    public void shouldHaveExceptionConsistencyWhenOnCloseToNull() {
        try {
            g.tx().onClose(null);
            fail("An exception should be thrown when onClose behavior is set to null");
        } catch (Exception ex) {
            validateException(Transaction.Exceptions.onCloseBehaviorCannotBeNull(), ex);
        }
    }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/structure/TransactionTest.java