code: public ManagementVertex getInputVertex(final int stage, final int index) {
  
  		if (stage >= this.stages.size()) {
  			return null;
  		}
  
  		return this.stages.get(stage).getInputManagementVertex(index);
  	}
docs: Returns the input vertex with the specified index for the given stage.
  
  @param stage
  the index of the stage
  @param index
  the index of the input vertex to return
  @return the input vertex with the specified index or <code>null</code> if no input vertex with such an index
  exists in that stage