I kept getting a crash after reloading a save (Factorio 0.14.20 and 0.14.21) and trying to use Crafting combinators.

Error message:
27.678 Error MainLoop.cpp:788: Exception at tick 5521: Error while running event on_built_entity (ID 6)
crafting_combinator/script/migration.lua:58: attempt to index upvalue '_ENV' (a nil value)

Managed to fix it, made a pull request on github:
https://github.com/theRustyKnife/CraftingCombinator/pull/2

Damn, I really should playtest more before releases... This is the second serious bug that I didn't know about since 0.3.
Anyway, thanks for fixing it, works well now.
Cheers TRK