Checks that this iterable has only one element, and returns that element.
Throws a StateError if this is empty or has more than one element.
E get single {
  if (isEmpty) {
    throw StateError('No such element');
  }
  if (_length > 1) {
    throw StateError('Too many elements');
  }
  return _first;
}
    © 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/LinkedList/single.html