code: public SoftwareSystem addSoftwareSystem(@Nonnull String name, @Nullable String description) {
          return addSoftwareSystem(Location.Unspecified, name, description);
      }
docs: Creates a software system (with an unspecified location) and adds it to the model.
  
  @param name        the name of the software system
  @param description a short description of the software system
  @return the SoftwareSystem instance created and added to the model (or null)
  @throws IllegalArgumentException if a software system with the same name already exists