Editor crashes on initialization when Table of Contents and ImageBlock is enabled

[Mgsy]

📝 Provide detailed reproduction steps (if any)

• Create a sample with the Table of Contents and ImageBlock plugins,
• Set the following initial data -

<h2 style="text-align:center;" id="ea849de114d74a69583adbe458569c912"><img class="image_resized" style="width:20.17%;" src="https://www.shutterstock.com/image-vector/sample-red-square-grunge-stamp-260nw-338250266.jpg"></h2>

• Initialize the editor

You can use the project I've created - toc-image-block-issue.zip

❌ Actual result

The editor doesn't initialize and throws the error:

ckeditorerror.ts:108 Uncaught (in promise) TypeError: Cannot read properties of null (reading 'getAttribute')
    at Vu (writer.ts:1815:29)
    at Iu.setAttribute (writer.ts:543:4)
    at Eh.<anonymous> (ckeditor5-premium-features.js:31:219346)
    at Eh.fire (emittermixin.ts:241:31)
    at Eh._convertItem (upcastdispatcher.ts:264:9)
    at Eh._convertChildren (upcastdispatcher.ts:314:24)
    at Object.convertChildren (upcastdispatcher.ts:174:64)
    at Ih.upcastDispatcher.on.priority (upcasthelpers.ts:503:54)
    at Eh.fire (emittermixin.ts:241:31)
    at Eh._convertItem (upcastdispatcher.ts:276:9)

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