I have only just setup this plugin and I have set about 10 spawn points. However the murderers continue to spawn even if they are not killed. This has led to areas being filled with them just standing around. And the /m.kill command does not work either, with the console spitting out this error:

Failed to call hook 'npcKill' on plugin 'Murderers v1.0.9' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Murderers.Kill () [0x0002a] in :0 
  at Oxide.Plugins.Murderers.npcKill (BasePlayer player, System.String command, System.String[] args) [0x00033] in :0 
  at Oxide.Plugins.Murderers.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x004ff] in :0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <9882f28dc2204b4dba514a9ad18f5042>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <9882f28dc2204b4dba514a9ad18f5042>:0 ​

Any help is appreciated