Cannot view audit logs when they contain entries with user id 0

src/Umbraco.Cms.Api.Management/Factories/AuditLogPresentationFactory.cs

@@ -1,5 +1,6 @@
 using Umbraco.Cms.Api.Management.ViewModels;
 using Umbraco.Cms.Api.Management.ViewModels.AuditLog;
+using Umbraco.Cms.Core;
 using Umbraco.Cms.Core.Models;
 using Umbraco.Cms.Core.Models.Membership;
 using Umbraco.Cms.Core.Services;
@@ -19,19 +20,17 @@ public AuditLogPresentationFactory(IUserService userService, IUserIdKeyResolver
 
     public IEnumerable<AuditLogResponseModel> CreateAuditLogViewModel(IEnumerable<IAuditItem> auditItems) => auditItems.Select(CreateAuditLogViewModel);
 
-    private AuditLogResponseModel CreateAuditLogViewModel(IAuditItem auditItem)
-    {
-        Guid userKey = _userIdKeyResolver.GetAsync(auditItem.UserId).GetAwaiter().GetResult();
-        IUser user = _userService.GetAsync(userKey).GetAwaiter().GetResult()
-                     ?? throw new ArgumentException($"Could not find user with id {auditItem.UserId}");
-
-        return new AuditLogResponseModel
+    private AuditLogResponseModel CreateAuditLogViewModel(IAuditItem auditItem) =>
+        new()
         {
             Comment = auditItem.Comment,
             LogType = auditItem.AuditType,
             Parameters = auditItem.Parameters,
             Timestamp = auditItem.CreateDate,
-            User = new ReferenceByIdModel(user.Key)
+            User = auditItem.UserId switch
+            {
+                Constants.Security.UnknownUserId => new ReferenceByIdModel(),
+                _ => new ReferenceByIdModel(_userIdKeyResolver.GetAsync(auditItem.UserId).GetAwaiter().GetResult()),
+            },
         };
-    }
 }

src/Umbraco.Core/Services/IUserIdKeyResolver.cs

@@ -5,14 +5,16 @@ public interface IUserIdKeyResolver
     /// <summary>
     /// Tries to resolve a user key to a user id without fetching the entire user.
     /// </summary>
-    /// <param name="key">The key of the user. </param>
-    /// <returns>The id of the user, null if the user doesn't exist.</returns>
+    /// <param name="key">The key of the user.</param>
+    /// <returns>The id of the user.</returns>
+    /// <exception cref="InvalidOperationException">Thrown when no user was found with the specified key.</exception>
     public Task<int> GetAsync(Guid key);
 
     /// <summary>
     /// Tries to resolve a user id to a user key without fetching the entire user.
     /// </summary>
-    /// <param name="id">The id of the user. </param>
-    /// <returns>The key of the user, null if the user doesn't exist.</returns>
+    /// <param name="id">The id of the user.</param>
+    /// <returns>The key of the user.</returns>
+    /// <exception cref="InvalidOperationException">Thrown when no user was found with the specified id.</exception>
     public Task<Guid> GetAsync(int id);
 }