public static IllegalArgumentException sideEffectKeyCanNotBeNull() {
            return new IllegalArgumentException("Side-effect key can not be null");
        }
Add the current {@link TraversalSideEffects} values, suppliers, and reducers to the provided {@link TraversalSideEffects}.
The implementation should (under the hood), use {@link TraversalSideEffects#registerIfAbsent(String, Supplier, BinaryOperator)} so that
if the argument {@link TraversalSideEffects} already has a registered supplier or binary operator, then don't overwrite it.

@param sideEffects the sideEffects to add this traversal's sideEffect data to.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/TraversalSideEffects.java