[Crash] bad argument #7 to 'fmt' (string expected, got nil)

[ghost]

Craftguide v1.8; MT v5.0.1; MTG v5.0.1; OS Debian 10

This happens with the binoculars:

ERROR[Main]: ServerError: AsyncErr: ServerThread::run Lua: Runtime error from mod 'craftguide' in callback on_playerReceiveFields(): .../craftguide/init.lua:621: bad argument #7 to 'fmt' (string expected, got nil)
ERROR[Main]: stack traceback:
ERROR[Main]: [C]: in function 'fmt'
ERROR[Main]: .../craftguide/init.lua:621: in function 'get_recipe_fs'
ERROR[Main]: .../craftguide/init.lua:724: in function 'make_formspec'
ERROR[Main]: .../craftguide/init.lua:734: in function 'show_fs'
ERROR[Main]: .../craftguide/init.lua:1008: in function 'fields'
ERROR[Main]: .../craftguide/init.lua:1041: in function '?'
ERROR[Main]: .../minetest/bin/../builtin/game/register.lua:419: in function <.../minetest/bin/../builtin/game/register.lua:399>

[kilbith]

Cannot reproduce. Please update the mod to the latest commit and retry.

[ghost]

Done, same as above:

Screenshot 1 https://imgur.com/PcDGTpW
Screenshot 2 https://imgur.com/adoDTrB
Gallery: https://imgur.com/a/E7QPXkQ

[kilbith]

Well, that doesn't make any sense, it shouldn't be nil at all. Anyway, retry with the last commit: 7a8b8d1

[ghost]

Tried, still having the same issue.
However it doesn't happen on Win7.

If it can be of any help I've checked which recipes produce that error, here is the image gallery (red = error): https://imgur.com/a/DgxIkOJ

I must say that I haven't checked each and every stair (pages 5-7) but I've randomly checked some of them so I think that it is safe to assume that all of them produce that error (assuming that the recipes are registered in the same manner for all of them, of course)... but I would not bet on it: e.g. some rails are safe, some are not.

[kilbith]

Retry with that: 732535c

[ghost]

Confirmed: error fixed.
I've checked each and every item in the creafting guide, they all passed the test.

Kudos, and thank you. :)