public static void validateSideEffectKey(final String key) throws IllegalArgumentException {
        if (null == key)
            throw TraversalSideEffects.Exceptions.sideEffectKeyCanNotBeNull();
        if (key.isEmpty())
            throw TraversalSideEffects.Exceptions.sideEffectKeyCanNotBeEmpty();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/util/SideEffectHelper.java