[Asterisk-Users] What causes this changethread error message?

[David Brodbeck]

I'm running Asterisk HEAD from March 4.  I've Googled a bit but I can't
figure out what causes this error:

app_queue.c:374 in changethread: Can't change device '**Unknown**' with no
technology!

It doesn't seem to be causing any problems, but I'm curious what causes it.
I did a few Google searches and found a lot of people asking about it, but
no real answers.