Newly made maps won't save and throw exceptions to the log, when reloading into the save all affected maps are permanently blank.

Maps should save their data and remain usable when the game is reloaded, as a map i created in the previous snapshot was able to while testing the issue.

Maps acted as expected until the world was save & quited then opened again.

Steps to Reproduce:
1. Create new map in snaphshot 23w44a
2. Save & Quit world.
3. Reload the same world.
4. Maps are all blank and do not fill out