On execute the /callheli Command i get this error:

Failed to call hook 'CallCommand' on plugin 'HeliScrap v1.5.1' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.HeliScrap.RemoveCost (BasePlayer player) [0x0009b] in <a99508bfd3ff4c3595881db3fde2b5e8>:0 
  at Oxide.Plugins.HeliScrap.CallCommand (BasePlayer player) [0x001b3] in <a99508bfd3ff4c3595881db3fde2b5e8>:0 
  at Oxide.Plugins.HeliScrap.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00132] in <a99508bfd3ff4c3595881db3fde2b5e8>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <795304323ac74a298b8ed190a1dfa739>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000de] in <beb2b64691c64e2b95b99491bd85442c>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <beb2b64691c64e2b95b99491bd85442c>:0