Board Thread:Lua Help/@comment-5068292-20150131070710/@comment-5068292-20150202121808

That gives the error:

Lua error in Module:Citation/CS1/Date_validation at line 300: attempt to call global 'is_set' (a nil value). Backtrace: Module:Citation/CS1/Date_validation:300: in function "dates" Module:Citation/CS1:1839: in function "dates" (tail call): ? mw.lua:425: ?