Empty paragraphs/whitespace with TinyMCE

**Describe the bug**
I've noticed this issue across applications like the WordPress classic editor and Jira Data Center.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to https://playground.wordpress.net/?plugin=classic-editor
2. Open the Hello World post
3. Type something in the editor
4. Update post
5. See empty paragraphs/whitespace

**Expected behavior**
No empty paragraphs/whitespace.

**Screenshots**
https://github.com/user-attachments/assets/70b91288-7784-45c3-b182-997ee96c932d

**Platform**
Zen Browser 1.17.14b (Firefox 146.0) (64-bit)

**Additional context**
Have not tried other browsers.

Reproduce the problem using the linked WordPress Playground classic-editor page and the listed steps, then trace the editor integration responsible for the saved content. Done means updating the post no longer leaves empty paragraphs or whitespace in the editor output; the issue does not name a source file or test to run.

Written by the indexing model from the issue text.