Occurs in visual studio code, using pandoc citer extension. Typing '@' in the editor throws an error, reporting the file 'default.yml' is missing.
Resolution is to provide the file. First, find the pandoc data directory:
% pandoc -v
pandoc 3.1.12.3
Features: +server +lua
Scripting engine: Lua 5.4
User data directory: /Users/dave/.local/share/pandoc
Copyright (C) 2006-2023 John MacFarlane. Web: https://pandoc.org
This is free software; see the source for copying conditions. There is no
warranty, not even for merchantability or fitness for a particular purpose.
Now, create that directory if required, and the missing file.
% mkdir ~/.local/share/pandoc # if required
% touch ~/.local/share/pandoc/defaults.yml
Restart visual studio and check it works -- type '@' in an editor. No error should be thrown and the extension should offer the list of citation codes as usual.