Was working on GUIShop and the attack heli comes by kills NPCs. 

Failed to call hook 'OnEntityTakeDamage' on plugin 'HumanNPC v0.3.46' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.HumanNPC.OnEntityTakeDamage (BaseCombatEntity entity, HitInfo hitinfo) [0x00013] in :0
  at Oxide.Plugins.HumanNPC.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00bbf] in :0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in :0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in :0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in :0

Getting same error spam console

13:13 [Error] Failed to call hook 'OnEntityTakeDamage' on plugin 'HumanNPC v0.3.47' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.HumanNPC.OnEntityTakeDamage (BaseCombatEntity entity, HitInfo hitinfo) [0x00013] in <10b52db9c65e447b9662da675151e939>:0
  at Oxide.Plugins.HumanNPC.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00bbf] in <10b52db9c65e447b9662da675151e939>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <d09a1f46ca2f4432811bcfe45ad13c7b>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <cf88a28c7fb44d36890d85a78331cc9d>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <cf88a28c7fb44d36890d85a78331cc9d>:0