code: func (g *Graph) removeVertex_locked(v *namedVertex) {
  	g.graph.RemoveNode(v)
  	delete(g.destinationEdgeIndex, v.ID())
  	delete(g.vertices[v.vertexType][v.namespace], v.name)
  	if len(g.vertices[v.vertexType][v.namespace]) == 0 {
  		delete(g.vertices[v.vertexType], v.namespace)
  	}
  }
docs: // must be called under write lock
  // removeVertex_locked removes the specified vertex from the graph and from the maintained indices.
  // It does nothing to indexes of neighbor vertices.