Returns true if this map contains the given value.
Returns true if any of the values in the map are equal to value according to the == operator.
bool containsValue(Object value) {
  for (K key in keys) {
    if (this[key] == value) return true;
  }
  return false;
}
    © 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/MapMixin/containsValue.html