anchor.diff:      }
     }
   
  -  /**
  -   * Creates a new Optional with the given value, if non-null.  Otherwise, returns an empty Optional.
  -   */
  +  /// Creates a new Optional with the given value, if non-null.  Otherwise, returns an empty Optional.
     factory Optional.ofNullable(T value) {
       if (value == null) {
         return empty.cast();
  
positive.code:   /// Returns an Optional provided by applying the mapper to this Optional's value, if present.  Otherwise, returns an empty Optional.
    Optional<R> flatMap<R>(Optional<R> mapper(T val));
  
    /**
     * Returns an Optional containing the result of applying the mapper to this Optional's value, if present.  Otherwise, returns an empty Optional.
     *
     * If the mapper returns a null value, returns an empty Optional.
     */
    Optional<R> map<R>(R mapper(T val));
  
    /// Returns this Optional's value, if present.  Otherwise, returns other.
  
negative.code:   /// Creates an empty Optional.
    const factory Optional.empty() = _Absent<T>._internal;
  
    /// The value associated with this Optional, if any.
    ///
    /// Throws [NoValuePresentError] if no value is present.
    T get value;
  
    /// Whether the Optional has a value.
  