[Bug] Empty nodes are not preserved

[wintercounter]

Initial checklist

• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected packages and versions

7.5.0

Link to runnable example

https://milkdown.dev/playground?text=DISwdgpgBAjAUAupJQExyA%3D%3D

Steps to reproduce

1. Add an empty line to Milkdown editor
2. Observe that Markdown in Codemirror gets updated correctly.
3. Make an edit in the markdown content.
4. Empty node gets removed.

Currently, when users edit their posts, they are losing the spacing between paragraphs because of this.

The markdown that gets saved into the database.

Line 1



Line 2

Upon edit we load the markdown into Milkdown, using (same code as in the playground)

const editor = get();
editor?.action((ctx) => {
  const view = ctx.get(editorViewCtx);
  const parser = ctx.get(parserCtx);
  const doc = parser(markdown);
  if (!doc) return;
  const state = view.state;
  view.dispatch(
    state.tr.replace(
      0,
      state.doc.content.size,
      new Slice(doc.content, 0, 0),
    ),
  );
});

Content becomes

Line 1

Line 2

Basically if I load again Milkdown's previous output, I won't get the same results again.

Expected behavior

Empty nodes are preserved by the parser.

Actual behavior

Empty node gets removed.

Runtime

Chrome

OS

Windows

Build and bundle tools

Next.js

[shenzhongkang]

face the same issue. @Saul-Mirone