Any N robbing happens at the soil surface, so it's minimal. If you live in an area that has earthworms, you'll find them at the juncture of soil/leaves, esp. if is damp. So that's a bonus.
Pile 'em on.

My garden thrives on shredded leaf mulch..like Alphonse said, pile it on!

Pam

I agree, I mulch every year & never add additional nitrogen.
But if it makes you sleep better, get some slow release organic nitrogen to put on the mulch.
Ether way, pile it on, mulch that is.

Because the sand I have for soil cannot hold much moisture without a lot of help I pile on the shredded leaves for mulch and the plants I grow thrive because those shredded leaves help retain soil moisture (in the root zone), help keep the soil cooler (which slows evaporation), helps suppress "weed" growth (does not totally eliminate it), and adds needed organic matter to the soil (which also helps the sand with moisture retention).
There will be no Nitrogen robbing because of the material you put on your soil as mulch contrary to what many people have been told. The research I have seen used to support this misconception has always had the mulch material mixed in to the soil.