Error in oxide log

[Error] Exception while calling NextTick callback (NullReferenceException: Object reference not set to an instance of an object.)
  at BaseEntity.SetParent (BaseEntity entity, System.UInt32 boneID, System.Boolean worldPositionStays, System.Boolean sendImmediate) [0x0013a] in <6a0cddd1b3834d348f4fc9ac7883d503>:0 
  at BaseEntity.SetParent (BaseEntity entity, System.String strBone, System.Boolean worldPositionStays, System.Boolean sendImmediate) [0x00010] in <6a0cddd1b3834d348f4fc9ac7883d503>:0 
  at Oxide.Plugins.UltimateLocker.PlaceLocker (BasePlayer player, BaseEntity entity, Oxide.Plugins.UltimateLocker+AutoLockPlayerSettingsData settings, System.Boolean sendMessage) [0x003d8] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Plugins.UltimateLocker.DeployLocker (BasePlayer player, BaseEntity entity, System.Boolean sendMessage) [0x00204] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Plugins.UltimateLocker+<>c__DisplayClass92_0.<OnEntitySpawned>b__1 () [0x00000] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <d59b507fd76240e5b62228d0eae39b73>:0 
20:51 [Error] Exception while calling NextTick callback (NullReferenceException: Object reference not set to an instance of an object.)
  at BaseEntity.SetParent (BaseEntity entity, System.UInt32 boneID, System.Boolean worldPositionStays, System.Boolean sendImmediate) [0x0013a] in <6a0cddd1b3834d348f4fc9ac7883d503>:0 
  at BaseEntity.SetParent (BaseEntity entity, System.String strBone, System.Boolean worldPositionStays, System.Boolean sendImmediate) [0x00010] in <6a0cddd1b3834d348f4fc9ac7883d503>:0 
  at Oxide.Plugins.UltimateLocker.PlaceLocker (BasePlayer player, BaseEntity entity, Oxide.Plugins.UltimateLocker+AutoLockPlayerSettingsData settings, System.Boolean sendMessage) [0x003d8] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Plugins.UltimateLocker.DeployLocker (BasePlayer player, BaseEntity entity, System.Boolean sendMessage) [0x00204] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Plugins.UltimateLocker+<>c__DisplayClass92_0.<OnEntitySpawned>b__1 () [0x00000] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <d59b507fd76240e5b62228d0eae39b73>:0 
20:51 [Error] Exception while calling NextTick callback (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.BetterTC+<>c__DisplayClass97_0.<TCSkinReplace>b__0 () [0x00195] in <4dcb07dc2ec24d94a3f607d598c93e03>:0 
  at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <d59b507fd76240e5b62228d0eae39b73>:0 

I got this error message in oxide log file. Its normal?

send your config file

Config file

UltimateLocker.json

Explain to me when this problem occurs, in detail.
What you were using, where you were positioning the locker, etc.

I haven't fixed yet what action causes the error. I found it when I was looking through the log for the day. But I still have a problem that another player can't install codelock on a generated machine in Spawn everything.