WHY IS THERE NO NIPPLE

*shrugs*

Maybe it's underneath her hair(third braid from the bottom), that looks big enough to conceal something...

But in all honesty, I bet the artist just forgot.

BARBE DOLL!

Really though, unless it's a "Collector's Item" or part of the Anime, They just do not draw the nipples even IF there is nothing really blocking them. Same holds true in the books ( Menasu being the biggest use of said rule... ).