public default <S> S getNullableScopeValue(final Pop pop, final String key, final Traverser.Admin<?> traverser) {
        try {
            return getScopeValue(pop, key, traverser);
        } catch (KeyNotFoundException nfe) {
            return null;
        }
    }
Calls {@link #getScopeValue(Pop, Object, Traverser.Admin)} and returns {@code null} if the key is not found.
Use this method with caution as {@code null} has one of two meanings as a return value. It could be that the
key was found and its value was {@code null} or it might mean that the key was not found and {@code null} was
simply returned.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/Scoping.java