You get that long and obscure URL while visiting google logged out, with no cookies.. So they all must be the defaults.
If they are the defaults, why put them in the URL?
If they are the defaults, why put them in the URL?
You've probably answered your own question there.
Eg: http://www.bing.com/search?q=test&qs=n&form=QBLH&...
Here, sk is "".
You can strip out empty fields with a bit of PHP (creating a new URL without the empty strings), which seems to work okay, but it's probably best not to risk the wrong effect, which is the end program seeing the empty fields wrongly (as NULL and not "").