Failed to call hook 'OnPlayerDeath' on plugin 'HuntRPG v1.7.9' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.HuntRPG.OnPlayerDeath (BasePlayer player, HitInfo hitInfo) [0x00052] in <4b4efb20766e4d89ad4ef7a77e13649e>:0
  at Oxide.Plugins.HuntRPG.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x002f4] in <4b4efb20766e4d89ad4ef7a77e13649e>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>: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

 heads up :)

Do you know what the circumstances were when this happened?

not a clue tho it has popped up a fair few times i'll see if i can catch what happens when this pops but here some info from logs if it helps, the only thing i had switched on the server when this started was infopanel  to magic panel 

Pulled from logs:-
First instance 

22/01/2021
17:12 [Error] Failed to call hook 'OnPlayerDeath'
17:12 [Info] [Death Notes] As scuba steve just found out, breathing underwater is rather difficult.
17:17 [Error] Failed to call hook 'OnPlayerDeath'
17:17 [Info] [Death Notes] scuba steve couldn't run away from the Wolf.

23/01/2021
17:58 [Error] Failed to call hook 'OnPlayerDeath'
17:58 [Info] [Death Notes] Harpo couldn't run away from the Bear.

24/01/2021
15:49 [Error] Failed to call hook 'OnPlayerDeath'
15:49 [Info] [Death Notes] aimbotGabba had enough of life.
15:57 [Error] Failed to call hook 'OnPlayerDeath'
15:57 [Info] [Death Notes] aimbotGabba couldn't run away from the Wolf.

26/01/2021
17:44 [Error] Failed to call hook 'OnPlayerDeath'
17:44 [Info] [Death Notes] fracking iriot had enough of life.
18:04 [Info] [Death Notes] fracking iriot did not want to be a part of the launa's experiments.
18:04 [Info] [Death Notes] A junior haunted down fracking iriot
18:04 [Error] Failed to call hook 'OnPlayerDeath'