Resolve "500 when error stack trace is empty"

What does this MR do?

This fixes a 500 error that would occur when loading the Error details page (Operations -> Error Tracking -> ) when the stack trace in the error is empty.

With this fixed the frontend can implement something to show the user when the stack trace is empty.

Before:

After:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #119205 (closed)