exception from 'b4 trailers -u'

Today I tried 'b4 trailers -u' and got this:

prentzel. b4 trailers -u
Calculating patch-ids from commits, this may take a moment... Checking change-id "20230209-submit-value-fixups-2023-3e7d7c6750af" Grabbing search results from inbox.sourceware.org Traceback (most recent call last):
File "/home/tromey/.local/bin/b4", line 8, in <module>

    sys.exit(cmd())

File "/home/tromey/.local/lib/python3.10/site-packages/b4/command.py", line 360, in cmd
cmdargs.func(cmdargs)
File "/home/tromey/.local/lib/python3.10/site-packages/b4/command.py", line 81, in cmd_trailers
b4.ez.cmd_trailers(cmdargs)
File "/home/tromey/.local/lib/python3.10/site-packages/b4/ez.py", line 1954, in cmd_trailers
update_trailers(cmdargs)
File "/home/tromey/.local/lib/python3.10/site-packages/b4/ez.py", line 862, in update_trailers
addtrailers = list(lmsg.followup_trailers)
AttributeError: 'NoneType' object has no attribute 'followup_trailers'

I don't know what it means. I do think there are some trailers to fetch; this was v3 of a series and I got some email with an approved-by for a few of the patches in it that weren't approved.

Tom