Failed to call hook 'OnItemAction' on plugin 'BlueprintShare v1.1.9' (NullReferenceException: Object reference not set to an instance of an object)
at Oxide.Plugins.BlueprintShare.CanShareBlueprint (BasePlayer sharer, System.String itemShortName) [0x00027] in <89ee23f04ed542b6a624c0a659b66eb3>:0
at Oxide.Plugins.BlueprintShare.OnItemAction (Item item, System.String action, BasePlayer player) [0x00072] in <89ee23f04ed542b6a624c0a659b66eb3>:0
at Oxide.Plugins.BlueprintShare.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00187] in <89ee23f04ed542b6a624c0a659b66eb3>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ec05e0208c9149bba43236ca58fea105>:0

What is the solution

I believe this error is being thrown because someone you are trying to share with doesn't exist for whatever reason. I will update the plugin with a patch that will add an error check to avoid this error being thrown. Could you also tell me how often you are receiving this error?

Today I got the error 4 times in a row, but there is no problem in the game

I have released the patch for a potential fix if you could download the new version and let me know if that has fixed the problem or if it is still happening.