void OnCrateHackEnd( HackableLockedCrate crate )
        {
            timer.In( config.timeToWait * 60, () => 
            {
                 // if crate will be killed before timer => NullReferenceException
                crate.inventory.Drop( "assets/prefabs/misc/item drop/item_drop.prefab", crate.GetDropPosition(), crate.transform.rotation );
                crate.Kill();
            } );
        }

Thanks for pointing that out, fixed!