Failed to call hook CanUpgrade

There are a lot of errors in the console. At the same time, I will say this. All player rights are disabled, meaning no one interacts with the plugin.

[Oxide] 21:35 [Error] Failed to call hook 'CanUpgrade' on plugin 'BetterTC v1.4.9' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.BetterTC.CanUpgrade (BasePlayer player, BuildingPrivlidge cup, BuildingBlock block, BuildingGrade+Enum grade) [0x00000] in <740b16b0919f432ea5e9090463f807ad>:0                                       38kb/s in, 497kb/s out
  at Oxide.Plugins.BetterTC.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00be9] in <740b16b0919f432ea5e9090463f807ad>: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 <8cb2d664f1574f2b96d53f1c1869d96a>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <8cb2d664f1574f2b96d53f1c1869d96a>:0

That's strange. From what I see, that error should occur when a build upgrade or reskin is in progress. Are you sure no one can use it?