message: docs(isDocument): add alternative of "$assertPopulated"
diff: @@ -27,6 +27,11 @@ class Cat {
  -> this could be minified, but for demonstration purposes this will stay the long version
  +:::tip
  +Alternatively, since mongoose 6.4.0, [`$assertPopulated`](https://mongoosejs.com/docs/api/document.html#document_Document-undefined) can also be used.
  +Note: the documentation link is currently broken and may change, see [mongoose #11957](https://github.com/Automattic/mongoose/issues/11957).
  +:::
  +
  ## isDocumentArray
  `isDocumentArray(doc: any[])` is the same as `isDocument`, only that it checks if it is an array **AND** all of the items are Documents.
  