code: public void add(ClassData classData) {
      checkRegistered(classData.type());
      innerClasses.put(classData.type(), classData);
    }
docs: Adds the data for an inner class.
  
  @throws java.lang.IllegalArgumentException if the class wasn't previous registered via {@link
  #registerInnerClass(String, int)} or {@link #registerInnerClassWithGeneratedName(String,
  int)}.