Pressing backspace on paragraph with a previous block with bullets results in error

[rioksane]

Describe the bug
Backspace paragraph to a previous block with bullets results in error

To Reproduce
Steps to reproduce the behavior:

1. Go to https://demo.plone.org/ or any othe new Plone 6.1 site
2. Add a new page
3. Add three paragraphs. Save
4. Change first paragraph to bullet list
5. Click before the second paragraph's first charater and click backspace
6. See error "Sorry, something went wrong with your request "

Screenshots

Software (please complete the following information):

• OSX
• Browser Firefox
  Volto 18.8.1
  Plone 6.1.0
  plone.restapi 9.11.0
  CMF 3.6
  Zope 5.12
  Python 3.12.9 (main, Feb 6 2025, 22:37:05) [GCC 12.2.0]
  PIL 11.0.0 (Pillow)

[ManojaD2004]

Not only that, when we have a text in the first block (not bullet text), and in the second block you have some text, take the cursor to beginning of second block and then press backspace button, you will see the content of first block is pushed to the content of second block (from left side).

[ManojaD2004]

I will work on this. I will fix both the bugs mentioned above.