Vehicle XML load failure for third-party mod storeItems causes Vehicle.lua crash (attempt to index nil with 'power')

[TheCodingDad-TisonK]

Description

When opening the UsedPlus finance dialog and clicking to pay off or close a loan, FS25 throws repeated errors attempting to load vehicle XML files from third-party mods. The crash cascades into a base-game Vehicle.lua error.

Log Output

Error: Failed to open xml file 'C:/Users/.../mods/FS25_SoilFertilizer/objects/liquidTank/uan32/liquidTank_uan32.xml'.
Error: Running LUA method 'update'.
dataS/scripts/vehicles/Vehicle.lua:2531: attempt to index nil with 'power'

Error: Failed to open xml file 'C:/Users/.../mods/FS25_SoilFertilizer/objects/liquidTank/uan32/liquidTank_uan32.xml'.
Error: Running LUA method 'mouseEvent'.
dataS/scripts/vehicles/Vehicle.lua:2531: attempt to index nil with 'power'

The errors trigger on both update (every frame) and mouseEvent (user clicks) — repeating dozens of times while the dialog is open.

Root Cause Analysis

• The referenced file (liquidTank_uan32.xml) is present in the mod's deployed zip — the file is not missing on our end.
• The mod (FS25_SoilFertilizer) is installed as a zip (FS25_SoilFertilizer.zip), not an extracted folder.
• The vehicle XML is registered as a <storeItem> in modDesc.xml, which UsedPlus appears to pick up and reference.
• When UsedPlus triggers a vehicle load (via the finance dialog interaction), FS25 fails to open the XML — likely because the path is being resolved as a raw filesystem path rather than through FS25's virtual filesystem (there is no physical FS25_SoilFertilizer/ folder, only the .zip).
• UsedPlus has no guard or pcall around the vehicle load failure, so the crash propagates to Vehicle.lua:2531.

Expected Behavior

If a vehicle XML fails to load (for any reason — missing mod, path resolution issue, corrupted entry), UsedPlus should handle the failure gracefully without crashing into Vehicle.lua. The item could be skipped or marked as unavailable.

Steps to Reproduce

1. Have FS25_SoilFertilizer installed (zip format) with a storeItem that uses a custom fill type
2. Open UsedPlus finance dialog
3. Click to pay off or close a loan — errors fire immediately and repeat

Environment

• FS25 version: current
• UsedPlus version: current
• FS25_SoilFertilizer v2.1.5.1 installed as zip
• Windows 11

[TheCodingDad-TisonK]

Follow-up: Source Code Analysis

After reading the UsedPlus source directly, I can pinpoint the exact issue more precisely.

Root Cause

VehicleSearchSystem.lua → generateUsedVehicleListingFromData() calls:

local storeItem = g_storeManager:getItemByXMLFilename(search.storeItemIndex)

This iterates all registered store items, including items from third-party mods that are vehicle type="pallet" with showInStore="false". Our liquidTank_uan32.xml is a fertilizer pallet, not a driveable vehicle — it's registered in modDesc.xml as a <storeItem> (required for the shop system to know about it) but explicitly hidden from the store with showInStore=false.

When a player somehow initiates a search/purchase for this pallet, VehicleSpawning.lua:spawnUsedVehicle() sends a BuyVehicleEvent:

-- Line 238-241
local success, err = pcall(function()
    g_client:getServerConnection():sendEvent(BuyVehicleEvent.new(buyData))
end)

The BuyVehicleEvent pcall covers the send, but not the server-side vehicle load. On the server, FS25 tries to open the pallet XML and fails — likely because vehicle type="pallet" with <parentFile> inheritance doesn't load correctly via the BuyVehicleEvent path (which is designed for driveable vehicles).

The half-initialized vehicle object persists and fires:

Vehicle.lua:2531: attempt to index nil with 'power'

on every update AND every mouseEvent — hence the repeated errors while the finance dialog is open.

Suggested Fixes

Option A (Recommended): Filter out non-driveable items when generating listings. Add to generateUsedVehicleListingFromData():

-- Skip non-driveable types and hidden store items
if storeItem.showInShop == false then return nil end
local vehicleType = storeItem.typeName or ""
if vehicleType == "pallet" or vehicleType == "placeable" then return nil end

Option B: Add a pcall guard around the server-side vehicle load callback in VehicleExtension.lua (wherever onBought processes the BuyVehicleEvent result).

Option C: Before calling BuyVehicleEvent, validate that the storeItem is a proper driveable vehicle:

-- In spawnUsedVehicle(), before sending BuyVehicleEvent:
if storeItem.typeName == "pallet" then
    UsedPlus.logError("Cannot spawn pallet-type item as used vehicle: " .. storeItem.xmlFilename)
    return false
end

Files to Check

• src/managers/usedvehicle/VehicleSearchSystem.lua — generateUsedVehicleListingFromData() — add pallet/hidden-item filter
• src/managers/usedvehicle/VehicleSpawning.lua — spawnUsedVehicle() — add type validation before BuyVehicleEvent
• src/gui/UsedSearchDialog.lua — should also filter out non-driveable items from the search UI