Never got this NRE when using Oxide, but does appear when running my server on the Carbon framework. Should be an easy fix
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Failed to call internal hook 'OnEntityBuilt' on plugin 'BGrade v1.1.5' [641201665] (Object reference not set to an instance of an object) at void Oxide.Plugins.BGrade.OnEntityBuilt(Planner plan, GameObject gameObject) in /home/rustadmin/New_Horizons/carbon/plugins/BGrade.cs:line 417 at object Oxide.Plugins.BGrade.InternalCallHook(uint hook, object[] args) in BGrade.cs/Internal:line 90