project zomboid error report: everytenminutes

java.lang.RuntimeException: __lt not defined for operand
        at se.krka.kahlua.vm.KahluaUtil.fail(KahluaUtil.java:83)
        at se.krka.kahlua.vm.KahluaThread.luaMainloop(KahluaThread.java:902)
        at se.krka.kahlua.vm.KahluaThread.call(KahluaThread.java:167)
        at se.krka.kahlua.vm.KahluaThread.pcall(KahluaThread.java:1922)
        at se.krka.kahlua.vm.KahluaThread.pcallvoid(KahluaThread.java:1777)
        at se.krka.kahlua.integration.LuaCaller.pcallvoid(LuaCaller.java:67)
        at se.krka.kahlua.integration.LuaCaller.protectedCallVoid(LuaCaller.java:130)
        at zombie.Lua.Event.trigger(Event.java:37)
        at zombie.Lua.LuaEventManager.triggerEvent(LuaEventManager.java:61)
        at zombie.GameTime.update(GameTime.java:1013)
        at zombie.gameStates.IngameState.UpdateStuff(IngameState.java:432)
        at zombie.gameStates.IngameState.update(IngameState.java:1370)
        at zombie.gameStates.GameStateMachine.update(GameStateMachine.java:101)
        at zombie.GameWindow.logic(GameWindow.java:688)
        at zombie.GameWindow.run(GameWindow.java:1315)
        at zombie.GameWindow.maina(GameWindow.java:1091)
        at zombie.gameStates.MainScreenState.main(MainScreenState.java:184)
1579772852222
1579772852227 -----------------------------------------
1579772852227 STACK TRACE
1579772852227 -----------------------------------------
1579772852227 function: update -- file: SMetalDrumGlobalObject.lua line # 151
1579772852228 function: checkRain -- file: SMetalDrumSystem.lua line # 44
1579772852228 function: EveryTenMinutes -- file: SMetalDrumSystem.lua line # 124