You get an error, even if you do things in the right way, at workflow creation. The reason is the graph need a Start and an End node, with a transition.
It is really not sweet to get an error alert when you do things in the right way: maybe we can remove the first check, since the workflow is not saved yet ?
Or have a start and end nodes with a default transition each time you create a workflow ? And maybe add a paragraph to explain why it is so important to have a start and end node.