@self and @home in the Page Tree macro root page display a "Not found" error

Issue Summary

The Page Tree macro allows you to set "@self" and "@home" as a parameter in the "Root Page" field, however when you start typing "@s" or "@h" the field displays and error saying "Not found".

Steps to Reproduce

1. Create a page
2. Add the Page Tree macro
3. In the "Root Page" field type "@self" or "@home"

Expected Results

No error should be displayed since this is a valid parameter.

Actual Results

The field displays a "Not found" error message.

Notes

This field usually returns page titles as you start typing some letters, but since it can't find any page which title starts with "@s" or "@h" it returns the error message.

Workaround

The macro can still be used as you can finish typing "@self" or "@home" and click the "Save" button, ignoring the error message, and after the page is published it should display the page tree accordingly.