Mod causes a crash if a loader is loading to/from or potentially just adjacent to a fluid wagon, since it attempts to grab the wagon's "cargo_wagon" inventory which doesn't exist.
Adding a check on line 112 of control.lua before calling loader_work() to make sure the inventory is not nil fixes this problem, and also resolves the issue for any other wagons (vanilla or modded) that don't have a "cargo_wagon" inventory.
