This is probably embarassingly easy to solve, but I couldn't find the solution.
I got the latest version of luaotfload from the git server, unpacked and installed.
And now, whenever I try to run mkluatexfontdb, I have this error: "attempt to index global 'caches' (a nil value)"
Here is the report:
$ mkluatexfontdb
luaotfload | Updating the font names database
luaotfload | Font names database not found, generating new one.
This can take several minutes; please be patient.
luaotfload | Updating the font names database
luaotfload | Scanning fonts known to operating system...
luaotfload | Scanning TEXMF fonts...
luaotfload | Scanning OS fonts..../otfl-font-nms.lua:740: attempt to index global 'caches' (a nil value)
Any hints?