Bug with simple persistent data [Solved]

[Regis]

I have a trivial code for merging persistent data that exactly same as in RenPy docs:

Code: Select all

    if persistent.gallery is None:
        persistent.gallery = set()

    def merge_gallery(old, new, current):
        current.update(old)
        current.update(new)

    renpy.register_persistent('gallery', merge_gallery)

And yet sometimes (rarely) it produces this exception for some players:

Code: Select all

I'm sorry, but an uncaught exception occurred.

While running game code:
  File "game/func_replay.rpy", line 90, in merge_gallery
AttributeError: 'NoneType' object has no attribute 'update'

-- Full Traceback ------------------------------------------------------------

Full traceback:
  File "C:\ZZZ\renpy\bootstrap.py", line 295, in bootstrap
    renpy.main.main()
  File "C:\ZZZ\renpy\main.py", line 490, in main
    renpy.persistent.update(True)
  File "C:\ZZZ\renpy\persistent.py", line 373, in update
    merge(other)
  File "C:\ZZZ\renpy\persistent.py", line 319, in merge
    val = merge_func(old, new, pval)
  File "game/func_replay.rpy", line 90, in merge_gallery
AttributeError: 'NoneType' object has no attribute 'update'

Windows-8-6.2.9200
Ren'Py 6.99.12.4.2187

1) Any ideas how that can happen? I want to understand what can possibly lead to this situation.
2) Am I doing something wrong? Is there a more proper way to work with set-like persistent object?

[Regis]

Upd: answer from renpytom: there is a bug in the docs. Merge function have to return merged value.

So the correct code should look like this:

Code: Select all

    def merge_gallery(old, new, current):
        current.update(old)
        current.update(new)
        return current