public final @NotNull Map<K, Collection<V>> toHashMap() {
    if (myMap instanceof HashMap) {
      //noinspection unchecked
      return (Map<K, Collection<V>>)((HashMap<K, Collection<V>>)myMap).clone();
    }
    else {
      return new HashMap<>(myMap);
    }
  }
public final @NotNull Map<K, Collection<V>> toHashMap()