@SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value
  static <K, V> ValueReference<K, V> unset() {
    return (ValueReference<K, V>) UNSET;
  }
@SuppressWarnings("unchecked") 
  static <K, V> ValueReference<K, V> unset() {
    return (ValueReference<K, V>) UNSET;
  }
@ SuppressWarnings ( "unchecked" ) // impl never uses a parameter or returns any non-null value static < K , V > ValueReference < K , V > unset ( ) { return ( ValueReference < K , V > ) UNSET ; }
Singleton placeholder that indicates a value is being loaded.
Singleton placeholder that indicates a value is being loaded .