docs: private Map<String, String> fillInitialVariables() {
          Map<String, TransitionTarget> targets = model.getChildren();
  
          Set<String> variables = new HashSet<>();
          for (TransitionTarget target : targets.values()) {
              OnEntry entry = target.getOnEntry();
              List<Action> actions = entry.getActions();
              for (Action action : actions) {
                  if (action instanceof Assign) {
                      String variable = ((Assign) action).getName();
                      variables.add(variable);
                  } else if (action instanceof SetAssignExtension.SetAssignTag) {
                      String variable = ((SetAssignExtension.SetAssignTag) action).getName();
                      variables.add(variable);
                  }
              }
          }
  
          Map<String, String> result = new HashMap<>();
          for (String variable : variables) {
              result.put(variable, "");
          }
  
          return result;
      }