docs: public Iterator<V> getServices(K key) {
          ComponentContext ctx = contextRef.get();
  
          if (ctx == null || key == null)
              return null;
  
          ConcurrentServiceReferenceSet<V> e = elementMap.get(key);
          if (e == null || e.isEmpty()) {
              return null;
          } else {
              return e.getServices();
          }
      }