public default Optional<Class<?>> getAnonymousTraversalClass() {
        return Optional.empty();
    }
Add a sack to be used throughout the life of a spawned {@link Traversal}.
This adds a {@link SackStrategy} to the strategies.

@param initialValue  the initial value of the sideEffect
@param mergeOperator the sack merge operator
@return a new traversal source with updated strategies
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/TraversalSource.java