Only overwrite path_prefix & path_type when not None
Only overwrite path_prefix & path_type when not None

Summary: This breaks internal functionality

Reviewed By: aartibasant

Differential Revision: D6975222

fbshipit-source-id: ce751950b4b9217d8ea5de703690451e98642f00

xzturn/caffe2,Yangqing/caffe2,Yangqing/caffe2,xzturn/caffe2,Yangqing/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,xzturn/caffe2,caffe2/caffe2,Yangqing/caffe2