nmh 1.8 has not been released yet, but the first release candidate is
out.  I haven't had time to test it yet, but a user has reported that
the mh-version command breaks with it.  That is, mh-version is only able
to report a few things before erroring out on a nil value where a string
was expected.

The attached patch fixes the problem and works on older nmh releases as
well as 1.8.  Is it okay for emacs-29? 

thanks,
mike