Cannot open citation key via with org-ref

Phenomenon

After I upgraded org-ref-20250828.2122 to org-ref-20251123.1710, I cannot open a BibTeX citation key any more in Org mode with the following message.

transient-setup: Symbol’s value as variable is void: $

Analysis

Enabling debug-on-error, I can see org-ref has migrated from hydra to transient for creating popup menus and it is the transient package that causes this problem.

Solution

Delete transient.elc in the folder elpa/transient-20251129.1551 and restart Emacs. Or reinstall this package via package-reinstall.

Lessons learnt

Do not update Emacs or its packages so often. If the current Emacs can work smoothly, just stick to it. Otherwise, fiddling with Emacs diverts our original focus on more important works.