return m.hashCode();
    }
  }

  // Test that we should get a distinct parameter error when doing equals test.
  static class ConstructorParameterWithOptionalNotInstantiable {
    public ConstructorParameterWithOptionalNotInstantiable(Optional<NotInstantiable> x) {
      checkNotNull(x);
    }

    @Override
    public boolean equals(@Nullable Object obj) {