A fork node does not require join. In the UML model, both nodes are independent from each other. I want to draw a diagram, in which I "split up" a flow using a join, but I do not want a join node to combine the flows again but a simple merge node instead. From the semantic point of view (activity diagrams use petri net semantics) this should be no problem, you can read the join as and and the merge as or. That is, I want to model that I split up a flow (into two flows), and I do not need both flows to process but only one.
In PlantUML, the fork requires an endfork. Basically, I want to use an endmerge or something like that.
An alternative solution would be to add a joinspec, like that: