code: public void addSubtypes(NamedType... subtypes) {
  
      if (this.subtypeList == null) {
        this.subtypeList = new ArrayList<>();
      }
      this.subtypeList.addAll(Arrays.asList(subtypes));
    }
docs: @see #setSubtypes(NamedType...)
  
  @param subtypes the {@link NamedType}s to add to {@link #setSubtypeList(List) sub-type list} for registration.