code: public B signal(String signalName) {
      SignalEventDefinition signalEventDefinition = createSignalEventDefinition(signalName);
      element.getEventDefinitions().add(signalEventDefinition);
  
      return myself;
    }
docs: Sets an event definition for the given signal name. If already a signal
  with this name exists it will be used, otherwise a new signal is created.
  
  @param signalName the name of the signal
  @return the builder object