docs: public static Map<Class<?>, Boolean> getHandlerTypes(Class<? extends MessageHandler> clazz) {
          Map<Class<?>, Boolean> types = new IdentityHashMap<>(2);
          for (Class<?> c = clazz; c != Object.class; c = c.getSuperclass()) {
              exampleGenericInterfaces(types, c, clazz);
          }
          if (types.isEmpty()) {
              throw JsrWebSocketMessages.MESSAGES.unknownHandlerType(clazz);
          }
          return types;
      }