Unclear warning when menu group does not exist

[Sebastian-ubs]

Describe the bug
When referencing a non-existing group (maybe because of a typo) the error message is unfortunately not giving enough hints.

"defaultWebViewTopMenu": {
    "items": [
      {
        ...
        "group": "extensionName-typo-in-here",
      }
    ]
}

leads to

[start:core] [1] 10:07:35 [extension host warning] 10:07:35.186 > Could not add menu contribution for website-viewer: TypeError: Cannot read properties of undefined (reading 'isExtensible') [at C:\code\paranext-core\src\extension-host\services\extension.service.ts:1131:18]
(website-viewer ist the extension name, not the column, group or menu entry name this is referring to)

To Reproduce
Steps to reproduce the behavior:

1. Implement this code in an extension
2. Watch the console output

Expected behavior
The warning should be "Could not add menu contribution for ...: A group with reference typo-in-here does not exist"