fix: add null guard for awareness state in createDecorations

[yuichi0301]

Problem

In createDecorations, awareness.getStates().forEach() iterates over
awareness states, but the state value (aw) can be null or undefined
(e.g. when a client disconnects). Accessing aw.cursor without a null
check causes a TypeError.

Solution

Added a null guard (aw &&) before accessing aw.cursor on line 98 of
src/plugins/cursor-plugin.js.

[yuichi0301]

Friendly ping 👋 @arnaugomez — would appreciate your eyes on this when you have a moment, since you recently worked on the cursor plugin in #8.

This is the y-tiptap counterpart of the same null-guard issue I'm also fixing in tiptap (ueberdosis/tiptap#7740): awareness.getStates() can contain transient null/undefined entries when clients disconnect, which causes a TypeError on aw.cursor. The fix is a one-line aw && guard.

Happy to add a test or iterate on the approach. Thanks!

[arnaugomez]

Hi! Thanks for your contribution.

Add a changeset and we'll merge. See contributing guide.

Besides, you can add a comment explaining why the null check, and that aw can be null when the client disconnects.

[yuichi0301]

@arnaugomez

Thanks for the review! I've pushed a follow-up commit (000bda2) addressing both points:

Added a .changeset/null-check-awareness-state.md patch entry
Added an inline comment explaining that aw can be null when a client disconnects, which is why the guard is needed
Let me know if you'd like any tweaks to the wording.