/**
   * Returns a representation of {@code a} as an instance of type {@code B}. If {@code a} cannot be
   * converted, an unchecked exception (such as {@link IllegalArgumentException}) should be thrown.
   *
   * @param a the instance to convert; will never be null
   * @return the converted instance; <b>must not</b> be null
   */
  @ForOverride
  protected abstract B doForward(A a);

  /**

  /**
   * Returns a representation of {@code a} as an instance of type {@code B}. If {@code a} cannot be
   * converted, an unchecked exception (such as {@link IllegalArgumentException}) should be thrown.
   *
   * @param a the instance to convert; will never be null
   * @return the converted instance; <b>must not</b> be null
   */
  @ForOverride
  protected abstract B doForward(A a);

  /**