Both not working,
When enter an not excisting page I get a blank page
This Blank page seems to be the the custom template which I made for the Pulse CMS which is integrated
You are over thinking the problem as Pulse will handle the error page for you automatically. By default if the CMS can’t locate the file reference in the URL it will try and load the ‘404’ page from the pages section. I suspect you’ve either deleted or renamed this page.