on server restart, I got this error spamming console. 

I did notice there has been an update but I figured I should at least document this.

Failed to call hook 'OnItemAddedToContainer' on plugin 'Headquarters v0.1.4' (NullReferenceException: Object reference not set to an instance of an object)

  at Oxide.Plugins.Headquarters.GetHeadquarterAtPosition (UnityEngine.Vector3 position) [0x00000] in <95959b3f56b34961b9caf59089c37980>:0

  at Oxide.Plugins.Headquarters.OnItemAddedToContainer (ItemContainer container, Item item) [0x00060] in <95959b3f56b34961b9caf59089c37980>:0

  at Oxide.Plugins.Headquarters.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00810] in <95959b3f56b34961b9caf59089c37980>:0

  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <e23ba2c0f246426296d81c842cbda3af>:0

  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <50629aa0e75d4126b345d8d9d64da28d>:0

  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <50629aa0e75d4126b345d8d9d64da28d>:0

Here is the log file for the same error. 

Failed to call hook 'OnItemAddedToContainer' on plugin 'Headquarters v0.1.4' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Headquarters.GetHeadquarterAtPosition (UnityEngine.Vector3 position) [0x00000] in <95959b3f56b34961b9caf59089c37980>:0 
  at Oxide.Plugins.Headquarters.OnItemAddedToContainer (ItemContainer container, Item item) [0x00060] in <95959b3f56b34961b9caf59089c37980>:0 
  at Oxide.Plugins.Headquarters.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00810] in <95959b3f56b34961b9caf59089c37980>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <e23ba2c0f246426296d81c842cbda3af>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <50629aa0e75d4126b345d8d9d64da28d>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <50629aa0e75d4126b345d8d9d64da28d>:0  
(Filename: C:\buildslave\unity\build\Runtime/Export/Debug/Debug.bindings.h Line: 39)

Thanks for reporting.  Should be fixed in the latest version.