removeAll method
Remove all their children from this render object's child list.
More efficient than removing them individually.
Implementation
@override
void removeAll(_PopUpList? popUpList) {
super.removeAll(popUpList);
final keepAliveBucket = _keepAliveBucket[popUpList]!;
keepAliveBucket.values.forEach((e) => dropChild(e));
keepAliveBucket.clear();
_keepAliveBucket.remove(popUpList);
}