Applies to 26.3, but also to all more recent versions as well.

Bug trigger:
1. Load ERC (e.g., open some IRC connection).
2. Open some channel or query, to have another ERC buffer.
3. Quit the server.
4. Make sure to kill the server buffer, if still there.
5. Launch ibuffer (e.g., type "M-x ibuffer"). Display stops mid-line on a line 
listing some ERC buffer linked to the quit server. Further buffer updates 
(typing 'g') trigger a crash for another reason (another fix to follow-up).

Root cause:
The erc-ibuffer's server column code will return nil in this case, since
the buffer associated to its process has been killed, making the server
information inacessible, and this is not tested properly.

Patch:
Attached.

-- 
Olivier Certner