popUntil method Null safety

void popUntil(
  1. RoutePredicate predicate
)

Calls pop repeatedly until the predicate returns true.

The predicate may be applied to the same route more than once if Route.willHandlePopInternally is true.

To pop until a route with a certain name, use the RoutePredicate returned from ModalRoute.withName.

The routes are closed with null as their return value.

See pop for more details of the semantics of popping a route.

link
Typical usage is as follows: 
void _doLogout() {
  navigator.popUntil(ModalRoute.withName('/login'));
}

Implementation

void popUntil(RoutePredicate predicate) {
  _RouteEntry? candidate = _history.cast<_RouteEntry?>().lastWhere(
    (_RouteEntry? e) => e != null && _RouteEntry.isPresentPredicate(e),
    orElse: () => null,
  );
  while(candidate != null) {
    if (predicate(candidate.route)) {
      return;
    }
    pop();
    candidate = _history.cast<_RouteEntry?>().lastWhere(
      (_RouteEntry? e) => e != null && _RouteEntry.isPresentPredicate(e),
      orElse: () => null,
    );
  }
}