Null value is converted to an empty object

When issuing `.save()` on an editor instance, properties with `null` as a value is converted to an empty object in the returned output.

Is this an intended feature of the editor? Is there some kind of flag where we can toggle this?

Expected behavior:
`null` should be a valid value for properties.

Editor.js version: 2.19.0

Plugins you use with their versions:
- @editorjs/delimiter: 1.1.0
- @editorjs/embed: 2.2.1
- @editorjs/header: 2.3.2
- @editorjs/list: 1.4.1
- @editorjs/paragraph: 2.6.1
- @editorjs/quote: 2.3.0
- @editorjs/raw: 2.1.2
- @editorjs/table: 1.2.2
- @editorjs/underline: 1.0.0
- editorjs-undo: 0.1.4
- Custom "ComponentPicker" plugin