[MC-307255] World migration generate a fallback null player when level has a Player tag with not data

If i use a world from 1.21.11 using a level.dat with Player tag but with not data in the migration to 26.1.1 a new file in players/data its created with a null UUID (00000000-0000-0000-0000-000000000000)

Steps to reproduce the issue

Create a world in 1.21.11 where a Player tag exists but contains no data

Expected result

The Player tag its ignored in the migration and continue the migration

Actual result

The Player tag its readed, pass the migration and create a fallback data, also create a new singleplayer data with invalid data.

Attachments

level.dat

Comments 4

Automation for Jira 2026-04-05T19:01:19Z

Thank you for helping us improve Minecraft! We saved your files:

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[Mod] ManosSef 2026-05-06T17:25:20Z

Is there a way for the game to create a level.dat file where the Player tag has no contents in 1.21.11, or do you have to edit the file manually?

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Doc 2026-05-12T15:53:57Z

Hi, i get a world with that issue but cannot find a way in recent versions to get that file with that things then not sure if maybe the issue come from a old version migration…

[Mod] ManosSef 2026-05-14T22:35:45Z

Resolving as Invalid, since there is no known way to get a vanilla client or server to create such a file, and the attached file indicates the world has previously been opened in a modified version.