Failed to call hook 'OnServerInitialized'

I get this when I load the plugin. 
No bosses spawn though
 

(20:46:20) | [BossMonster] Loading files on the /oxide/data/BossMonster/Bosses/ path has started...
(20:46:20) | [BossMonster] File Derek the Delivery Guy has been loaded successfully!
(20:46:20) | [BossMonster] File Frankenstein has been loaded successfully!
(20:46:20) | [BossMonster] File Lord Luscious has been loaded successfully!
(20:46:20) | [BossMonster] File Negan has been loaded successfully!
(20:46:20) | [BossMonster] File Officer Grimes has been loaded successfully!
(20:46:20) | [BossMonster] File Rainbow Randy has been loaded successfully!
(20:46:20) | [BossMonster] File Ratatouille has been loaded successfully!
(20:46:20) | [BossMonster] File Super Mark has been loaded successfully!
(20:46:20) | [BossMonster] File Wolfgang has been loaded successfully!
(20:46:20) | [BossMonster] Loading files on the /oxide/data/BossMonster/CustomMap/ path has started...
(20:46:21) | [BossMonster] File 12G-generated2 has been loaded successfully!
(20:46:21) | Failed to call hook 'OnServerInitialized' on plugin 'BossMonster v2.1.5' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.BossMonster.GetNameMonument (MonumentInfo monument) [0x00155] in <996e017da1a44d9b9a986bdffe41167f>:0 
  at Oxide.Plugins.BossMonster.IsNecessaryMonument (MonumentInfo monument) [0x00006] in <996e017da1a44d9b9a986bdffe41167f>:0 
  at Oxide.Plugins.BossMonsterExtensionMethods.ExtensionMethods.Where[TSource] (System.Collections.Generic.IEnumerable`1[T] source, System.Func`2[T,TResult] predicate) [0x00016] in <996e017da1a44d9b9a986bdffe41167f>:0 
  at Oxide.Plugins.BossMonster.OnServerInitialized () [0x0004d] in <996e017da1a44d9b9a986bdffe41167f>:0 
  at Oxide.Plugins.BossMonster.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x006fa] in <996e017da1a44d9b9a986bdffe41167f>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <42f9bedc659b4f4786eb778d3cd58968>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000de] in <112d89ea5d3348c8b949af0ab1a866d2>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <112d89ea5d3348c8b949af0ab1a866d2>:0
(20:46:21) | Loaded plugin BossMonster v2.1.5 by KpucTaJl