@CanIgnoreReturnValue
  public final @Nullable R invoke(@Nullable T receiver, @Nullable Object... args)
      throws InvocationTargetException, IllegalAccessException {
    return (R) invokeInternal(receiver, checkNotNull(args));
  }

  /** Returns the return type of this {@code Invokable}. */
  // All subclasses are owned by us and we'll make sure to get the R type right.
  @SuppressWarnings("unchecked")