code: public boolean has(final K key) {
  		if (this.services.containsKey(key)) {
  			final Collection<S> collection = this.services.get(key);
  
  			if (collection == null) {
  				return false;
  			}
  
  			if (collection.isEmpty()) {
  				return false;
  			}
  
  			return true;
  		}
  
  		return false;
  	}
docs: Determines whether there are any current services that have the given
  key.
  
  @param key
  The key to search for.
  @return True if there is at least one registered service with the given
  key, and false otherwise.