code: public ManagementGroupVertex getOutputGroupVertex(int index) {
  
  		final Iterator<ManagementGroupVertex> it = this.groupVertices.iterator();
  		while (it.hasNext()) {
  
  			final ManagementGroupVertex groupVertex = it.next();
  			if (groupVertex.isOutputVertex()) {
  				if (index == 0) {
  					return groupVertex;
  				} else {
  					--index;
  				}
  			}
  		}
  
  		return null;
  	}
docs: Returns the output group vertex in this stage with the given index. Output group vertices are those vertices
  which have outgoing edges to group vertices of a higher stage.
  
  @param index
  the index of the output group vertex to return
  @return the output group vertex with the given index or <code>null</code> if no such vertex exists