In stgit/commands/mail.py on line 668 it says:

        message_str = stack.patchs[pn].data.message_str

I think this should be:

        message_str = stack.patches[pn].data.message_str

This causes the following abort when I try to mail some patches:

Error: Unhandled exception:
Traceback (most recent call last):
File "/usr/lib/python3.10/site-packages/stgit/main.py", line 183, in _main
return command.func(parser, options, args)
File "/usr/lib/python3.10/site-packages/stgit/commands/mail.py", line 853, in func
msg_id = __send_message('cover', tmpl, options, patches)
File "/usr/lib/python3.10/site-packages/stgit/commands/mail.py", line 415, in __send_message
msg = __build_cover(tmpl, msg_id, options, patches)
File "/usr/lib/python3.10/site-packages/stgit/commands/mail.py", line 668, in __build_cover
message_str = stack.patchs[pn].data.message_str
AttributeError: 'Stack' object has no attribute 'patchs'