code: void registerExecutionVertex(final ExecutionVertex vertex) {
  
  		if (this.vertexMap.put(vertex.getID(), vertex) != null) {
  			throw new IllegalStateException("There is already an execution vertex with ID " + vertex.getID()
  				+ " registered");
  		}
  	}
docs: Registers an execution vertex with the execution graph.
  
  @param vertex
  the execution vertex to register