Cleanup unknown user for audit events

src/Umbraco.Core/Compose/AuditEventsComponent.cs

@@ -44,20 +44,22 @@ namespace Umbraco.Core.Compose
         public void Terminate()
         { }
 
+        internal static IUser UnknownUser => new User { Id = Constants.Security.UnknownUserId, Name = Constants.Security.UnknownUserName, Email = "" };
+
         private IUser CurrentPerformingUser
         {
             get
             {
                 var identity = Thread.CurrentPrincipal?.GetUmbracoIdentity();
                 var user = identity == null ? null : _userService.GetUserById(Convert.ToInt32(identity.Id));
-                return user ?? new User { Id = 0, Name = "SYSTEM", Email = "" };
+                return user ?? UnknownUser;
             }
         }
 
         private IUser GetPerformingUser(int userId)
         {
             var found = userId >= 0 ? _userService.GetUserById(userId) : null;
-            return found ?? new User {Id = 0, Name = "SYSTEM", Email = ""};
+            return found ?? UnknownUser;
         }
 
         private string PerformingIp

src/Umbraco.Core/Constants-Security.cs

@@ -15,13 +15,18 @@ namespace Umbraco.Core
             public const int SuperUserId = -1;
 
             /// <summary>
-            /// The id for the 'unknown' user
+            /// The id for the 'unknown' user.
             /// </summary>
             /// <remarks>
             /// This is a user row that exists in the DB only for referential integrity but the user is never returned from any of the services
             /// </remarks>
             public const int UnknownUserId = 0;
 
+            /// <summary>
+            /// The name of the 'unknown' user.
+            /// </summary>
+            public const string UnknownUserName = "SYTEM";
+
             public const string AdminGroupAlias = "admin";
             public const string SensitiveDataGroupAlias = "sensitiveData";
             public const string TranslatorGroupAlias = "translator";

src/Umbraco.Web/Compose/BackOfficeUserAuditEventsComponent.cs

@@ -1,5 +1,6 @@
 using System;
 using Umbraco.Core;
+using Umbraco.Core.Compose;
 using Umbraco.Core.Composing;
 using Umbraco.Core.Models.Membership;
 using Umbraco.Core.Services;
@@ -39,7 +40,7 @@ namespace Umbraco.Web.Compose
         private IUser GetPerformingUser(int userId)
         {
             var found = userId >= 0 ? _userService.GetUserById(userId) : null;
-            return found ?? new User { Id = 0, Name = "SYSTEM", Email = "" };
+            return found ?? AuditEventsComponent.UnknownUser;
         }
 
         private static string FormatEmail(IMembershipUser user)