Change errors string output to null on eval
Change errors string output to null on eval

Glass only checks that an error string is null on the output of eval, not
that it is null or empty. I fixed this in glass but it got lost when I
moved the changes from git to tfs in the OOB branch. This change makes
MIEngine work with glasses eval.

upsoft/MIEngine,faxue-msft/MIEngine,wesrupert/MIEngine,xingshenglu/MIEngine,bbqchickenrobot/MIEngine,Microsoft/MIEngine,chuckries/MIEngine,phofman/MIEngine,jacdavis/MIEngine,pieandcakes/MIEngine,upsoft/MIEngine,UIKit0/MIEngine,wesrupert/MIEngine,faxue-msft/MIEngine,gregg-miskelly/MIEngine,Microsoft/MIEngine,enginekit/MIEngine,conniey/MIEngine,xincun/MIEngine,edumunoz/MIEngine,csiusers/MIEngine,edumunoz/MIEngine,yacoder/MIEngine,wesrupert/MIEngine,vosen/MIEngine,rajkumar42/MIEngine,enginekit/MIEngine,idkwim/MIEngine,caslan/MIEngine,orbitcowboy/MIEngine,wiktork/MIEngine,faxue-msft/MIEngine,kelltrick/MIEngine,devilman3d/MIEngine,xincun/MIEngine,devilman3d/MIEngine,pieandcakes/MIEngine,UIKit0/MIEngine,caslan/MIEngine,thurday/MIEngine,idkwim/MIEngine,yacoder/MIEngine,gregg-miskelly/MIEngine,bbqchickenrobot/MIEngine,idkwim/MIEngine,faxue-msft/MIEngine,orbitcowboy/MIEngine,pieandcakes/MIEngine,edumunoz/MIEngine,caslan/MIEngine,jacdavis/MIEngine,kelltrick/MIEngine,xingshenglu/MIEngine,rajkumar42/MIEngine,csiusers/MIEngine,edumunoz/MIEngine,orbitcowboy/MIEngine,chuckries/MIEngine,PistonDevelopers/MIEngine,phofman/MIEngine,caslan/MIEngine,jacdavis/MIEngine,rajkumar42/MIEngine,pieandcakes/MIEngine,wiktork/MIEngine,xingshenglu/MIEngine,orbitcowboy/MIEngine,conniey/MIEngine,yazeng/MIEngine,enginekit/MIEngine,csiusers/MIEngine,gregg-miskelly/MIEngine,yacoder/MIEngine,yazeng/MIEngine,UIKit0/MIEngine,bbqchickenrobot/MIEngine,upsoft/MIEngine,csiusers/MIEngine,kelltrick/MIEngine,conniey/MIEngine,devilman3d/MIEngine,xincun/MIEngine,devilman3d/MIEngine,wiktork/MIEngine,yazeng/MIEngine,chuckries/MIEngine,Microsoft/MIEngine,rajkumar42/MIEngine,Microsoft/MIEngine,thurday/MIEngine,wesrupert/MIEngine,phofman/MIEngine,chuckries/MIEngine,thurday/MIEngine