[Flutter] Don't use 'BuildContext's across async gaps

Don't use 'BuildContext's across async gaps. 

 

this error is BuildContext Optional error.

 

may be thid code.

if (isLogin) {
  Navigator.pop(context, "success");
}

 

 

you must use mounted.

if (mounted) {
  if (isLogin) {
    Navigator.pop(context, "success");
  }