Might want to extend that elseif with a plain else case under it with addToModCategory(part,"Control/RCS/[something goes here]"), or there will be other missing RCS parts... Strange though, if resourceName is nil, then that means that the RCS has no fuel, thus no category? --RCS for rcs in modulesByName(part,"ModuleRCS") do if containsNodeTypeName(rcs,"resourceName","MonoPropellant") then addToModCategory(part,"Control/RCS/MonoPropellant") elseif rcs.values.resourceName == nil then addToModCategory(part,"Control/RCS/Misc") else addToModCategory(part,"Control/RCS/"..rcs.values.resourceName,rcs.values.resourceName, "Categories/Control/RCS_Misc") end end Maybe something like that? *Did not test.