With ListStyles enabled, modeling throws TypeError if a list is preceded by non-tagged content

[KevinMc]

📝 Provide detailed reproduction steps (if any)

We've got a variety of legacy HTML data created with older rich text editors, some of which contains elements that aren't surrounded by element tags. For example:

If there are missing paragraph or other tags prior to a list
<ol>
    <li>Item one</li>
</ol>
Then the editor won't model

1. Given the above source HTML data
2. Load an editor with the ListStyles plugin enabled

✔️ Expected result

The content should be modeled and editable by the editor.

❌ Actual result

A TypeError occurs:

TypeError: Cannot read property 'getAttribute' of null
    at Tm (ckeditor.js:5)
    at Pm.setAttribute (ckeditor.js:5)
    at Yp.t.on.priority (ckeditor.js:5)
    at Yp.fire (ckeditor.js:5)
    at Yp._convertItem (ckeditor.js:5)
    at Yp._convertChildren (ckeditor.js:5)
    at Yp.<anonymous> (ckeditor.js:5)
    at Yp.fire (ckeditor.js:5)
    at Yp._convertItem (ckeditor.js:5)
    at Yp._convertChildren (ckeditor.js:5)

If the ListStyles plugin is disabled, then the editor functions as expected.

📃 Other details

• Browser: Chrome 86
• OS: macOS 10.15
• CKEditor version: 22.0.x
• Installed CKEditor plugins: Bold, Italics, List, ListStyles
• Build ID: eom5f2mlp9sw-494y9pll8mj2

[sanchonarancho]

the same problem in my build:

There was a problem initializing the editor. CKEditorError: i is null Read more: https://ckeditor.com/docs/ckeditor5/latest/framework/guides/support/error-codes.html#error-i is null
    pc writer.js:1487
    setAttribute writer.js:380
    init liststyleediting.js:218
    fire emittermixin.js:209
    _convertItem upcastdispatcher.js:249
    _convertChildren upcastdispatcher.js:282
    Ha upcasthelpers.js:448
    fire emittermixin.js:209
    _convertItem upcastdispatcher.js:249
    _convertChildren upcastdispatcher.js:282
    Ha upcasthelpers.js:448
    fire emittermixin.js:209
    _convertItem upcastdispatcher.js:253
    convert upcastdispatcher.js:207
    toModel datacontroller.js:414
    change model.js:178
    toModel datacontroller.js:413
    parse datacontroller.js:395
    init datacontroller.js:314
    _runPendingChanges model.js:830
    enqueueChange model.js:236
    init datacontroller.js:311
    decorate observablemixin.js:255
    fire emittermixin.js:209
    t observablemixin.js:259
    create classiceditor.js:209
    promise callback*create/< classiceditor.js:200
    create classiceditor.js:194
    <anonymous> index.html:34

html:

    <p>
       www
    </p>

    qqq

    <p>
       eee
    </p>

    <ul>
        <li>rrr</li>
    </ul>
    <p>
       ttt
    </p>

[FilipTokarski]

Hi, thanks for the report. I can confirm this bug. If I remove the ListStyle plugin, everything works fine ( even with normal List plugin ).
cc @pomek

[Mgsy]

Short copy/paste line for a quick reproduction:

editor.setData( `If there are missing paragraph or other tags prior to a list
<ol>
    <li>Item one</li>
</ol>
Then the editor won't model` )