i typed in a name of a person who was not on the server as a test and got this 

Failed to call hook 'SCmdCheckPlayer' on plugin 'ServerArmour v0.0.83' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ServerArmour.SCmdCheckPlayer (Oxide.Core.Libraries.Covalence.IPlayer player, System.String command, System.String[] args) [0x00094] in <23cd487aed2b47cfb94c9814b2ee24f2>:0                              1kb/s in, 9kb/s out
  at Oxide.Plugins.ServerArmour.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0171f] in <23cd487aed2b47cfb94c9814b2ee24f2>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <efb9a8684e344ecfa065c7b416e6d2fd>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <b0a93b504f034a0db8b1c3d2503c0987>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <b0a93b504f034a0db8b1c3d​

Thank you for reporting this to me

Merged post

This should now be fixed in v0.0.84