Change 657847 had a related patch set uploaded (by Umherirrender; owner: Umherirrender):
[mediawiki/core@master] Use always filled rev_user_text on Special:MergeHistory

https://gerrit.wikimedia.org/r/657847

Change 657847 merged by jenkins-bot:
[mediawiki/core@master] Use always filled rev_user_text on Special:MergeHistory

https://gerrit.wikimedia.org/r/657847

Is this resolved?

This is an active and recently reported production error. If it is resolved, please confirm so in Logstash or by evaluating the code change relative to the error report and closing if it seems resolved. @daniel might be able to help with this area of code.

I suspect that this is caused by an empty (or otherwise invalid) user name in the revision history somewhere. I wrote a fix for a similar issue last week, see T232451: ParameterAssertionException: "Bad value for parameter $title: invalid name" (affects actions info, history, diff).

The code that logs the issue is behaving correctly, reporting data corruption. The only thing we can do here is fix the data. Perhaps we could have a script that finds some invalid user name (like the empty string) in the actor table, and replaces and references to that actor with the "Unknown user" actor. Such a script could optionally also take a known actor ID. The relevant entry in the actor table should probably be deleted once all references have been removed. Or the name could be replaced by something valid, like "Unknown User 8743".

In T272635#6796369, @daniel wrote:

I suspect that this is caused by an empty (or otherwise invalid) user name in the revision history somewhere. I wrote a fix for a similar issue last week, see T232451: ParameterAssertionException: "Bad value for parameter $title: invalid name" (affects actions info, history, diff).

The code that logs the issue is behaving correctly, reporting data corruption. The only thing we can do here is fix the data. Perhaps we could have a script that finds some invalid user name (like the empty string) in the actor table, and replaces and references to that actor with the "Unknown user" actor. Such a script could optionally also take a known actor ID. The relevant entry in the actor table should probably be deleted once all references have been removed. Or the name could be replaced by something valid, like "Unknown User 8743".

No, it was using a null value from a join while the name of the ip also in the result set. But the problem from the linked bug can also happen on Special:MergeHistory with invalid names in the user table. But the root cause was a null, not the empty string.

The patch set is already merged, but I have not closed the ticked to allow tracking if backporting was needed or not. But new train should be out there and logstash hopefully clean about this error

The code to fill the LinkBatch is in SpecialMergeHistory and it is in SpecialCheckUserLog, that means it is another issue. Only the part which trigger the error is the same, because both using the same class to fill the cache.

Would suggest to have an own task to also have correct tags

Maybe it is related to T275669, but that depends on the value after encountered invalid title: in the log message, which is not provided here in the stacktrace, but from the code it could be the same database field.