return unmodifiableCollectionSubclass(createCollection());
  }

  /**
   * Creates the collection of values for a single key.
   *
   * <p>Collections with weak, soft, or phantom references are not supported. Each call to {@code
   * createCollection} should create a new instance.
   *
   * <p>The returned collection class determines whether duplicate key-value pairs are allowed.
   *

    return unmodifiableCollectionSubclass(createCollection());
  }

  /**
   * Creates the collection of values for a single key.
   *
   * <p>Collections with weak, soft, or phantom references are not supported. Each call to {@code
   * createCollection} should create a new instance.
   *
   * <p>The returned collection class determines whether duplicate key-value pairs are allowed.
   *