Construct default functions by passing nothing rather than 0
Construct default functions by passing nothing rather than 0

Because MSVC's implementation of `std::function` is really not a big fan of passing in `0`, more specifically, it errors at the end of a 15 deep template chain. Constructing it by passing nothing solves the problem.

SergeyMakarenko/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,facebook/fbthrift,LinusU/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,LinusU/fbthrift,LinusU/fbthrift,facebook/fbthrift,getyourguide/fbthrift,facebook/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,Orvid/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,facebook/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,facebook/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,Orvid/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,Orvid/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,Orvid/fbthrift,getyourguide/fbthrift,facebook/fbthrift,facebook/fbthrift,getyourguide/fbthrift