Several segments of belt-highlighter.lua do a similar piece of code (look up an array and add to it), but only one of those segments (lines 721-726) checks to make sure it exists beforehand. This adds similar checks to every other instance, fixing the error.
Several segments of belt-highlighter.lua do a similar piece of code (look up an array and add to it), but only one of those segments (lines 721-726) checks to make sure it exists beforehand. This adds similar checks to every other instance, fixing the error.
See also this discussion thread on the Factorio mod portal.