Get the first key in the map. Returns null if the map is empty.
K firstKey() {
  if (_root == null) return null;
  return _first.key;
}
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dart.dev/stable/2.5.0/dart-collection/SplayTreeMap/firstKey.html