mount -t null fails

[Thomas Klausner <wiz%NetBSD.org@localhost>]

I've just updated to 6.99.4and now mount -t null -r over a tmpfs fails:

# ls -ld /bin
drwxr-xr-x  2 root  wheel  1024 Apr  8 19:53 /bin
# ls -ld /home/wiz/sandbox/bin
drwxr-xr-x  2 root  wheel  0 Sep  3  2009 /home/wiz/sandbox/bin
# mount -t null -r /bin sandbox/bin                                             
                                                                                
                                                 
mount: makeraw failed: Inappropriate file type or format
# mount -t null -r /bin /home/wiz/sandbox/bin 
mount: makeraw failed: Inappropriate file type or format
# mount | grep sandbox
tmpfs on /home/wiz/sandbox type tmpfs (local)

This worked for years. Please fix!

Thanks,
 Thomas