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

[lauraneto]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes #17149

Description

When using the IContentService it is possible to pass in user id 0 (special Unknown/System user). This user does not actually exist in the database, and was therefore causing an exception to be thrown in IUserIdKeyResolver, which was called when mapping the audit logs.
It was not mentioned in the reported issue, but when reproducing the issue I noticed it only happened with user 0, any other non-existing id would throw a foreign key error when trying to insert, so this was a special case.

Reproduction steps

1. Create a node in the backoffice.
2. Add code to use the ContentService to publish the node, using user id 0, and call it.
   In my case I added a simple API endpoint that I could easily call as needed, and added the following code. You can also check the reproduction sample provided in the issue.

IContent content = _contentService.GetById(Guid.Parse("3b2f86e4-5839-440f-985e-4e0e02c05289")) ?? throw new InvalidOperationException();
content.SetValue("field", Guid.NewGuid().ToString());
_contentService.Save(content, 0);
_contentService.Publish(content, ["*"], 0);

3. Open the node in the backoffice and go to the info tab.

Current behavior

The audit logs do not load and an error toast is shown.

New behavior

The audit logs load and show the entries with id 0 as Unknown.

[lauraneto]

As the user service does no extra validations when retrieving the user, I removed this call entirely, as it seemed unnecessary as we only need the key.

[Copilot]

Pull Request Overview

This PR updates the audit log functionality to properly handle audit entries for the special Unknown/System user (user id 0).

• Updates the IUserIdKeyResolver documentation to indicate that an exception is thrown when a user is not found.
• Modifies the AuditLogPresentationFactory to return an empty user reference when the user id is the unknown/system user, avoiding an exception.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Umbraco.Core/Services/IUserIdKeyResolver.cs	Updated XML comments to document the new exception-based behavior when a user is not found.
src/Umbraco.Cms.Api.Management/Factories/AuditLogPresentationFactory.cs	Refactored audit log view model creation to handle user id 0 gracefully using a switch expression.

[Zeegaan]

Looks good, tests good 🎉