This started showing up yesterday:

Exception while calling NextTick callback (ArgumentNullException: Value cannot be null. Parameter name: key) at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) [0x00008] in :0 at System.Collections.Generic.Dictionary`2[TKey,TValue].TryGetValue (TKey key, TValue& value) [0x00000] in :0 at ItemManager.FindItemDefinition (System.String shortName) [0x00005] in :0 at Oxide.Plugins.BackPumpJack+c__AnonStorey0.<>m__0 () [0x002f7] in <3bc37d8fe0c745efa63c88d4c8ade21f>:0 at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in :0

Check your config

I figured it out. Thanks