Have a look for this respond:
Failed to call hook 'OnEntityDeath' on plugin 'HitIcon v2.0.0'
(NullReferenceException: Object reference not set to an instance of an object)
at Oxide.Plugins.HitIcon.SendDeath (BaseCombatEntity entity, HitInfo info) [0x00073] in :0
at Oxide.Plugins.HitIcon.OnEntityDeath (BaseCombatEntity entity, HitInfo info) [0x00000] in :0
at Oxide.Plugins.HitIcon.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00187] in :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 