当REQUEST_URI可以为空时？

I was creating router for my PHP website and came across such a method :

public function getURI() {
   if (!empty($_SERVER["REQUEST_URI"])) {
      // do some stuff and return the result
   }
}

I figured out even if I request 'example.com' - $_SERVER["REQUEST_URI"] is not empty (it's '/')

The questions are:

Why do I need to check whether the $_SERVER["REQUEST_URI"] is empty?

When REQUEST_URI can be empty?

In a HTTP call, $_SERVER["REQUEST_URI"] is never empty, because it's a part of the HTTP protocol.

If this function is called in CLI, $_SERVER["REQUEST_URI"] could be empty.

edit

Or, as pointed by @ArtisticPhoenix, it can be changed by the user unset($_SERVER["REQUEST_URI"]); or $_SERVER["REQUEST_URI"]="foo";