docs: public Set<T> getDependents(T element) {
        lock.readLock().lock();
        try {
           Set<T> dependants = this.incomingEdges.get(element);
           if (dependants == null || dependants.isEmpty()) {
              return new HashSet<>();
           }
           return Collections.unmodifiableSet(this.incomingEdges.get(element));
        } finally {
           lock.readLock().unlock();
        }
  
     }