code: @Nullable
    public static Object triggerSynchronous (@Nonnull final IEvent aEvent)
    {
      ValueEnforcer.notNull (aEvent, "Event");
  
      final ICommonsList <Object> aRetValues = new CommonsArrayList <> ();
      // for all scopes
      for (final EScope eCurrentScope : EScope.values ())
      {
        // get current instance of scope
        final IScope aScope = _getScope (eCurrentScope, false);
        if (aScope != null)
        {
          // get event manager (may be null)
          final InternalScopedEventManager aEventMgr = _getEventMgr (aScope);
          if (aEventMgr != null)
          {
            // main event trigger
            aRetValues.add (aEventMgr.triggerSynchronous (aEvent));
          }
        }
      }
      return aEvent.getResultAggregator ().apply (aRetValues);
    }
docs: Notify observers without sender and without parameter.
  
  @param aEvent
  The event on which observers should be notified.
  @return The aggregated result object.