Rendering error when inserting a Root parameter in Children Macro which prevents displaying children

Steps to reproduce

1. Edit the Sandbox.WebHome page in WYSIWYG mode
2. Click on Insert > Other Macros > Children
3. Click 'Select'
4. Insert a Root parameter, like xwiki:Sandbox
5. Click 'Submit'

Expected results

The macro is inserted with the children being displayed. No errors occur in the logs.

Actual results

The following error is displayed in XWiki console:

2025-04-28 19:04:16,501 [http-nio-1115-exec-2 - http://localhost:1115/xwiki/bin/get/Sandbox/WebHome?] ERROR o.a.v.rendering                - Left side ($childNodeIds.size()) of comparison operation has null value at xwiki:XWiki.DocumentTreeMacros[line 179, column 29]

No pages are displayed on the macro.