code: @Deprecated
      public void addRequestHandler(RequestHandler requestHandler) {
          checkMutability();
          requestHandler2s.add(RequestHandler2.adapt(requestHandler));
      }
docs: @deprecated by {@link #addRequestHandler(RequestHandler2)}.
  
  Appends a request handler to the list of registered handlers that are run
  as part of a request's lifecycle.
  
  @param requestHandler
  The new handler to add to the current list of request
  handlers.