Update NULL to null
Update NULL to null

Summary: `null` is more Hack friendly.

Test Plan: no-op

Reviewed By: eugene@fb.com

Subscribers: trunkagent, alandau, mshneer

FB internal diff: D1761664

Tasks: 5811982

Signature: t1:1761664:1420216271:62978ee690e9637419509eb38ed026674fe9387e

guker/fbthrift,project-zerus/fbthrift,soumith/fbthrift,fengshao0907/fbthrift,getyourguide/fbthrift,project-zerus/fbthrift,soumith/fbthrift,sinjar666/fbthrift,sinjar666/fbthrift,uber/fbthrift,LinusU/fbthrift,HankFaan/fbthrift,LinusU/fbthrift,guker/fbthrift,raphaelamorim/fbthrift,maxwell-demon/fbthrift,LinusU/fbthrift,sinjar666/fbthrift,maxwell-demon/fbthrift,project-zerus/fbthrift,kangkot/fbthrift,facebook/fbthrift,chjp2046/fbthrift,HankFaan/fbthrift,Orvid/fbthrift,LinusU/fbthrift,chjp2046/fbthrift,Orvid/fbthrift,getyourguide/fbthrift,maxwell-demon/fbthrift,HankFaan/fbthrift,SergeyMakarenko/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,Orvid/fbthrift,chjp2046/fbthrift,maxwell-demon/fbthrift,HankFaan/fbthrift,HankFaan/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,sinjar666/fbthrift,maxwell-demon/fbthrift,LinusU/fbthrift,sinjar666/fbthrift,uber/fbthrift,project-zerus/fbthrift,chjp2046/fbthrift,SergeyMakarenko/fbthrift,project-zerus/fbthrift,facebook/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,guker/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,raphaelamorim/fbthrift,raphaelamorim/fbthrift,kangkot/fbthrift,project-zerus/fbthrift,maxwell-demon/fbthrift,Orvid/fbthrift,raphaelamorim/fbthrift,Orvid/fbthrift,Orvid/fbthrift,uber/fbthrift,soumith/fbthrift,sinjar666/fbthrift,getyourguide/fbthrift,kangkot/fbthrift,chjp2046/fbthrift,kangkot/fbthrift,HankFaan/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,raphaelamorim/fbthrift,sinjar666/fbthrift,guker/fbthrift,chjp2046/fbthrift,kangkot/fbthrift,soumith/fbthrift,chjp2046/fbthrift,facebook/fbthrift,facebook/fbthrift,getyourguide/fbthrift,uber/fbthrift,project-zerus/fbthrift,fengshao0907/fbthrift,getyourguide/fbthrift,HankFaan/fbthrift,kangkot/fbthrift,project-zerus/fbthrift,guker/fbthrift,raphaelamorim/fbthrift,SergeyMakarenko/fbthrift,HankFaan/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,maxwell-demon/fbthrift,facebook/fbthrift,maxwell-demon/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,SergeyMakarenko/fbthrift,Orvid/fbthrift,project-zerus/fbthrift,fengshao0907/fbthrift,uber/fbthrift,project-zerus/fbthrift,Orvid/fbthrift,soumith/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,guker/fbthrift,soumith/fbthrift,guker/fbthrift,soumith/fbthrift,kangkot/fbthrift,LinusU/fbthrift,soumith/fbthrift,kangkot/fbthrift,raphaelamorim/fbthrift,Orvid/fbthrift,chjp2046/fbthrift,HankFaan/fbthrift,guker/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,chjp2046/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,fengshao0907/fbthrift,raphaelamorim/fbthrift,uber/fbthrift,SergeyMakarenko/fbthrift,kangkot/fbthrift,maxwell-demon/fbthrift,HankFaan/fbthrift,fengshao0907/fbthrift,soumith/fbthrift,guker/fbthrift,kangkot/fbthrift,chjp2046/fbthrift,uber/fbthrift,chjp2046/fbthrift,fengshao0907/fbthrift,uber/fbthrift,maxwell-demon/fbthrift,raphaelamorim/fbthrift,facebook/fbthrift,soumith/fbthrift,LinusU/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,raphaelamorim/fbthrift,HankFaan/fbthrift,fengshao0907/fbthrift,kangkot/fbthrift,facebook/fbthrift,fengshao0907/fbthrift,uber/fbthrift,chjp2046/fbthrift,facebook/fbthrift,project-zerus/fbthrift,fengshao0907/fbthrift,project-zerus/fbthrift,raphaelamorim/fbthrift,fengshao0907/fbthrift,fengshao0907/fbthrift,maxwell-demon/fbthrift,soumith/fbthrift,sinjar666/fbthrift,guker/fbthrift,guker/fbthrift