New error message with Dovecot/Pigeonhole

[Jerry]

FreeBSD 11.1 / amd64
dovecot --version 2.3.2 (582970113)
Pigeonhole version 0.5.2 (7704de5e)

I have run 'sieve-test" many times to check out changes in my "sieve" scripts.
This morning, it suddenly started issuing this error message:

sieve-test(root): Fatal: Couldn't drop privileges: User is missing UID (see mail_uid setting)

I am not sure what is wrong or how to correct it, since it never happened
before.

-- 
Jerry

"Ainsi sera, groigne qui groigne"