Test for predicate existence before enumeration
Test for predicate existence before enumeration

appunite/Objective-LevelDB,matehat/Objective-LevelDB,i-miss-you/Objective-LevelDB,jinjian1991/Objective-LevelDB,fullstackclub/Objective-LevelDB,akkakks/Objective-LevelDB,lsm/LevelDB-ObjC,jinjian1991/Objective-LevelDB,cureHsu/Objective-LevelDB,cureHsu/Objective-LevelDB,i-miss-you/Objective-LevelDB,uber/Objective-LevelDB,matehat/Objective-LevelDB,jinjian1991/Objective-LevelDB,fullstackclub/Objective-LevelDB,yincheng1988/Objective-LevelDB,i-miss-you/Objective-LevelDB,yincheng1988/Objective-LevelDB,uber/Objective-LevelDB,yincheng1988/Objective-LevelDB,uber/Objective-LevelDB,appunite/Objective-LevelDB,appunite/Objective-LevelDB,cureHsu/Objective-LevelDB,cybertk/Objective-LevelDB,lsm/LevelDB-ObjC,uber/Objective-LevelDB,matehat/Objective-LevelDB,cureHsu/Objective-LevelDB,cybertk/Objective-LevelDB,fullstackclub/Objective-LevelDB,lsm/LevelDB-ObjC,cybertk/Objective-LevelDB,i-miss-you/Objective-LevelDB