TYPO3 Core

[FE][pageNotFound_handling] is empty per Default, which means requests for non-existing/accessible pages will be handled by linking upwards in the page tree.

If you create a page which is a "shortcut of first subpage", but has no subpages, a 404 exception is thrown instead of the upwards linking.
The configurations 'false' and '0' are also handled differently.
The behaviour for 'true' and '1' is correct.