Saving a structure with a name containing two consecutive dots (..) logs the error
This is likely caused by the code trying to load the structure from data packs. Loading them from and saving them to the generated/<namespace>/structures folder of a world works fine.
Either way two consecutive dots can form perfectly valid paths when they are in the middle (e.g. a..b) or at the beginning (e.g. ..a) of a path piece, therefore this check should be more precisely and the error message should include, that this is data pack related only.
- Open the structure block GUI and click "SAVE"
- Look at the log
→ The following error appeared