Exception trhown after inserting '/' slash in middle of text

[LucasXu0]

Bug Description
inserting '/' slash in middle of text causes exception.

How to Reproduce
Go to any line including text and insert '/' in the middle of the text.

Expected Behavior
To insert '/' and show slash command menu or at least not throw exception.

Operating System
Arch Linux

AppFlowy Version(s)
Exists on AppFlowy-IO/AppFlowy@4c0168d commit

Screenshots
No response

Additional Context
Probably the root cause are changes in this commit.

Reference: AppFlowy-IO/AppFlowy#1997