Same issue like it was here: https://umod.org/community/planterbox-defender/42113-failed-to-call-hook-error

Failed to call hook 'OnGrowableGather' on plugin 'PlanterboxDefender v2.1.0'
(NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.PlanterboxDefender.CanLootGrowableEntity (GrowableEntity plant, BasePlayer player) [0x00046] in <74ac879ef5b44eb98bf3f2daf66762d3>:0
 
  at Oxide.Plugins.PlanterboxDefender.OnGrowableGather (GrowableEntity plant, BasePlayer player) [0x00000] in <74ac879ef5b44eb98bf3f2daf66762d3>:0

  at Oxide.Plugins.PlanterboxDefender.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00038] in <74ac879ef5b44eb98bf3f2daf66762d3>:0

  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <23ba99f131254889867c71f0bd137b1d>:0

  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <157a94ee66ab4a7991faecd1eb84be3b>:0

  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <157a94ee66ab4a7991faecd1eb84be3b>:0​

I think somewhere in code need to check for null value. For GrowableEntity or BasePlayer.

So I am added this to the first line inside function object CanLootGrowableEntity(GrowableEntity plant, BasePlayer player):

if (plant == null || player == null) return null;​