public default E generateFinalResult(final S preCap) {
        return (E) preCap;
    }
Post-process the side-effect and return the post-processed side-effect.
The default implementation is simply the identity function and returns the argument.

@param preCap the pre-processed side-effect.
@return the post-processed side-effect.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/Generating.java