code: public Route to(Controller controller, Method method) {
          Preconditions.checkNotNull(controller);
          Preconditions.checkNotNull(method);
          this.controller = controller;
          this.controllerMethod = method;
          if (!method.getReturnType().isAssignableFrom(Result.class)) {
              throw new IllegalArgumentException(ERROR_CTRL + method + ERROR_IN + controller
                      .getClass() + "`, or the method does not return a " + Result.class.getName() + " object");
          }
          return _build();
      }
docs: Sets the targeted action method of the resulting route.
  
  @param controller the controller object, must not be {@literal null}.
  @param method     the method name, must not be {@literal null}.
  @return the current route builder