使用 setViewControllers 时异常

当我使用 FDFullscreenPopGesture 有以下跳转需求时
NSMutableArray *controllerArr = [self.navigationController.viewControllers mutableCopy];

```
if (controllerArr.count) {
[controllerArr removeAllObjects];
}

[controllerArr addObject:self.navigationController.viewControllers[0]];

[controllerArr addObject:[[FirstViewController alloc] init]];

[controllerArr addObject:[[SecondViewController alloc] init]];

[self.navigationController setViewControllers:controllerArr animated:YES];
```

当我 Push 到SecondViewController后,在UINavigationController+FDFullscreenPopGesture.m 在
[self fd_pushViewController:viewController animated:animated] 地方抛出异常,求解