code: public static void setDefaultBus(Bus bus) {
          synchronized (BusFactory.class) {
              if (bus == null) {
                  defaultBus = null;
              } else {
                  defaultBus = bus;
              }
          }
      }
docs: Provide a new implemented static method for setting the default Bus.
  The static method from parent class BusFactory also tries to change the thread bus, which is not required.
  Use BusFactory.class as the synchronized lock due to the signature of the BusFactory.setDefaultBus is
  public static void synchronized setDefaultBus(Bus bus)
  
  @param bus