This spams my console 20+ times each time BetterNpc plugin loads.

Exception while calling NextTick callback (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.HealthyGuns.RepairContainerContents (LootContainer container) [0x00006] in <083f0d1587ac4198bcf3deb91854aa16>:0 
  at Oxide.Plugins.HealthyGuns+<>c__DisplayClass4_0.<OnLootSpawn>b__0 () [0x00000] in <083f0d1587ac4198bcf3deb91854aa16>:0 
  at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <15f61ddda771464d8246ebdce8ff4811>:0

Got help from BetterNpc Support that seems to work fine.

Added this code to plugin file (bold text):

private void RepairContainerContents(LootContainer container)
        {
            if (container == null || container.inventory == null) return;
			
            foreach (Item item in container.inventory.itemList)
            {
                if (item != null && item.hasCondition && item.condition != item.info.condition.max && ItemOfCategory(item, ItemCategory.Weapon))
                    item.condition = item.info.condition.max;
            }
        }