Version: 1.8.5-2-gd337622
Either the pattern is incorrect or debugstack() does not supply the output you'd expect.
Unfortunately debugstack() does trim the path if it's too long, as can be seen in the error message below. LibGraph had the exact same problem, the only thing that helps is to shorten the path (i.e. the folder names, move up within the folder structure or similar).

...uttonAuras\libs\SharedMedia_ButtonHighlight\SMBH.lua:37: attempt to concatenate a nil value