make use of the new nullable expression result by returning null from some sema errors.
make use of the new nullable expression result by returning null from some sema errors.

Swift SVN r75

KrishMunot/swift,hooman/swift,MukeshKumarS/Swift,xwu/swift,devincoughlin/swift,swiftix/swift,cbrentharris/swift,Ivacker/swift,dduan/swift,slavapestov/swift,MukeshKumarS/Swift,Jnosh/swift,russbishop/swift,deyton/swift,shahmishal/swift,shajrawi/swift,huonw/swift,amraboelela/swift,arvedviehweger/swift,nathawes/swift,glessard/swift,codestergit/swift,parkera/swift,jtbandes/swift,amraboelela/swift,rudkx/swift,gmilos/swift,jmgc/swift,tinysun212/swift-windows,gribozavr/swift,nathawes/swift,Ivacker/swift,gribozavr/swift,xwu/swift,sschiau/swift,bitjammer/swift,codestergit/swift,amraboelela/swift,kperryua/swift,tardieu/swift,modocache/swift,frootloops/swift,emilstahl/swift,uasys/swift,jckarter/swift,apple/swift,rudkx/swift,djwbrown/swift,tardieu/swift,gmilos/swift,huonw/swift,SwiftAndroid/swift,dduan/swift,sschiau/swift,ahoppen/swift,practicalswift/swift,shajrawi/swift,benlangmuir/swift,LeoShimonaka/swift,mightydeveloper/swift,brentdax/swift,ken0nek/swift,shahmishal/swift,calebd/swift,tjw/swift,dduan/swift,jmgc/swift,kentya6/swift,kusl/swift,felix91gr/swift,austinzheng/swift,LeoShimonaka/swift,SwiftAndroid/swift,atrick/swift,KrishMunot/swift,tkremenek/swift,devincoughlin/swift,KrishMunot/swift,JaSpa/swift,cbrentharris/swift,swiftix/swift.old,jtbandes/swift,harlanhaskins/swift,tjw/swift,aschwaighofer/swift,bitjammer/swift,modocache/swift,brentdax/swift,Ivacker/swift,modocache/swift,austinzheng/swift,kentya6/swift,tinysun212/swift-windows,khizkhiz/swift,practicalswift/swift,mightydeveloper/swift,brentdax/swift,swiftix/swift,allevato/swift,shajrawi/swift,IngmarStein/swift,kperryua/swift,hughbe/swift,hooman/swift,JaSpa/swift,sdulal/swift,gribozavr/swift,roambotics/swift,modocache/swift,jmgc/swift,tkremenek/swift,ken0nek/swift,calebd/swift,uasys/swift,manavgabhawala/swift,CodaFi/swift,zisko/swift,frootloops/swift,tardieu/swift,xedin/swift,aschwaighofer/swift,slavapestov/swift,CodaFi/swift,hughbe/swift,bitjammer/swift,atrick/swift,gribozavr/swift,felix91gr/swift,gregomni/swift,gottesmm/swift,gmilos/swift,jckarter/swift,sdulal/swift,deyton/swift,swiftix/swift,milseman/swift,MukeshKumarS/Swift,manavgabhawala/swift,therealbnut/swift,milseman/swift,LeoShimonaka/swift,zisko/swift,austinzheng/swift,jmgc/swift,jckarter/swift,djwbrown/swift,therealbnut/swift,danielmartin/swift,MukeshKumarS/Swift,devincoughlin/swift,kstaring/swift,zisko/swift,jtbandes/swift,dreamsxin/swift,xwu/swift,deyton/swift,gottesmm/swift,MukeshKumarS/Swift,khizkhiz/swift,codestergit/swift,KrishMunot/swift,kstaring/swift,amraboelela/swift,swiftix/swift,hooman/swift,tardieu/swift,tjw/swift,jopamer/swift,kusl/swift,jtbandes/swift,ahoppen/swift,Jnosh/swift,shajrawi/swift,kstaring/swift,stephentyrone/swift,shahmishal/swift,alblue/swift,JGiola/swift,devincoughlin/swift,roambotics/swift,gregomni/swift,adrfer/swift,emilstahl/swift,harlanhaskins/swift,kperryua/swift,modocache/swift,arvedviehweger/swift,CodaFi/swift,milseman/swift,gribozavr/swift,IngmarStein/swift,OscarSwanros/swift,ben-ng/swift,khizkhiz/swift,mightydeveloper/swift,emilstahl/swift,xedin/swift,gmilos/swift,lorentey/swift,LeoShimonaka/swift,djwbrown/swift,shahmishal/swift,zisko/swift,atrick/swift,JGiola/swift,cbrentharris/swift,amraboelela/swift,benlangmuir/swift,hughbe/swift,austinzheng/swift,glessard/swift,frootloops/swift,stephentyrone/swift,sschiau/swift,dduan/swift,cbrentharris/swift,allevato/swift,xwu/swift,JGiola/swift,alblue/swift,gribozavr/swift,kentya6/swift,Jnosh/swift,lorentey/swift,atrick/swift,modocache/swift,calebd/swift,huonw/swift,djwbrown/swift,shajrawi/swift,kentya6/swift,modocache/swift,benlangmuir/swift,arvedviehweger/swift,djwbrown/swift,devincoughlin/swift,mightydeveloper/swift,rudkx/swift,natecook1000/swift,khizkhiz/swift,xedin/swift,kentya6/swift,aschwaighofer/swift,parkera/swift,khizkhiz/swift,felix91gr/swift,hooman/swift,airspeedswift/swift,mightydeveloper/swift,karwa/swift,JaSpa/swift,roambotics/swift,swiftix/swift,zisko/swift,jckarter/swift,zisko/swift,allevato/swift,JGiola/swift,Ivacker/swift,gottesmm/swift,gribozavr/swift,tkremenek/swift,parkera/swift,xedin/swift,manavgabhawala/swift,alblue/swift,kstaring/swift,djwbrown/swift,alblue/swift,lorentey/swift,xedin/swift,shahmishal/swift,kusl/swift,harlanhaskins/swift,russbishop/swift,slavapestov/swift,return/swift,IngmarStein/swift,tkremenek/swift,austinzheng/swift,return/swift,shajrawi/swift,practicalswift/swift,allevato/swift,lorentey/swift,KrishMunot/swift,dduan/swift,swiftix/swift.old,aschwaighofer/swift,uasys/swift,jmgc/swift,airspeedswift/swift,apple/swift,LeoShimonaka/swift,OscarSwanros/swift,stephentyrone/swift,jckarter/swift,MukeshKumarS/Swift,felix91gr/swift,adrfer/swift,swiftix/swift.old,benlangmuir/swift,cbrentharris/swift,alblue/swift,tinysun212/swift-windows,arvedviehweger/swift,alblue/swift,russbishop/swift,aschwaighofer/swift,tinysun212/swift-windows,adrfer/swift,karwa/swift,practicalswift/swift,codestergit/swift,kperryua/swift,tkremenek/swift,parkera/swift,milseman/swift,allevato/swift,hooman/swift,shahmishal/swift,MukeshKumarS/Swift,russbishop/swift,calebd/swift,kentya6/swift,return/swift,alblue/swift,frootloops/swift,karwa/swift,SwiftAndroid/swift,harlanhaskins/swift,therealbnut/swift,ahoppen/swift,swiftix/swift.old,shahmishal/swift,CodaFi/swift,stephentyrone/swift,ben-ng/swift,karwa/swift,calebd/swift,gmilos/swift,atrick/swift,sdulal/swift,swiftix/swift.old,nathawes/swift,Ivacker/swift,slavapestov/swift,JaSpa/swift,austinzheng/swift,austinzheng/swift,hooman/swift,therealbnut/swift,uasys/swift,deyton/swift,glessard/swift,kusl/swift,harlanhaskins/swift,gottesmm/swift,johnno1962d/swift,felix91gr/swift,jtbandes/swift,danielmartin/swift,gregomni/swift,xwu/swift,jopamer/swift,danielmartin/swift,sdulal/swift,natecook1000/swift,karwa/swift,return/swift,bitjammer/swift,jopamer/swift,ben-ng/swift,tjw/swift,amraboelela/swift,milseman/swift,gregomni/swift,dduan/swift,russbishop/swift,brentdax/swift,manavgabhawala/swift,airspeedswift/swift,roambotics/swift,Ivacker/swift,hughbe/swift,khizkhiz/swift,kusl/swift,gottesmm/swift,johnno1962d/swift,adrfer/swift,benlangmuir/swift,aschwaighofer/swift,brentdax/swift,stephentyrone/swift,russbishop/swift,arvedviehweger/swift,ken0nek/swift,emilstahl/swift,milseman/swift,adrfer/swift,sdulal/swift,shajrawi/swift,airspeedswift/swift,practicalswift/swift,KrishMunot/swift,jckarter/swift,uasys/swift,khizkhiz/swift,adrfer/swift,gmilos/swift,natecook1000/swift,return/swift,jmgc/swift,SwiftAndroid/swift,Jnosh/swift,Jnosh/swift,djwbrown/swift,cbrentharris/swift,ken0nek/swift,danielmartin/swift,tjw/swift,rudkx/swift,tinysun212/swift-windows,huonw/swift,calebd/swift,nathawes/swift,johnno1962d/swift,gregomni/swift,kentya6/swift,brentdax/swift,zisko/swift,rudkx/swift,deyton/swift,bitjammer/swift,return/swift,IngmarStein/swift,JaSpa/swift,stephentyrone/swift,sschiau/swift,nathawes/swift,ahoppen/swift,swiftix/swift.old,xwu/swift,harlanhaskins/swift,sdulal/swift,johnno1962d/swift,slavapestov/swift,apple/swift,kusl/swift,huonw/swift,practicalswift/swift,sschiau/swift,gottesmm/swift,IngmarStein/swift,kentya6/swift,aschwaighofer/swift,airspeedswift/swift,tkremenek/swift,manavgabhawala/swift,bitjammer/swift,Jnosh/swift,emilstahl/swift,natecook1000/swift,hughbe/swift,felix91gr/swift,codestergit/swift,IngmarStein/swift,SwiftAndroid/swift,brentdax/swift,danielmartin/swift,dduan/swift,russbishop/swift,kperryua/swift,gottesmm/swift,SwiftAndroid/swift,rudkx/swift,ben-ng/swift,OscarSwanros/swift,shajrawi/swift,bitjammer/swift,roambotics/swift,lorentey/swift,devincoughlin/swift,Ivacker/swift,deyton/swift,sschiau/swift,emilstahl/swift,kusl/swift,OscarSwanros/swift,milseman/swift,OscarSwanros/swift,johnno1962d/swift,ben-ng/swift,roambotics/swift,johnno1962d/swift,xedin/swift,kperryua/swift,huonw/swift,tinysun212/swift-windows,Ivacker/swift,therealbnut/swift,frootloops/swift,allevato/swift,sdulal/swift,adrfer/swift,therealbnut/swift,IngmarStein/swift,tinysun212/swift-windows,sschiau/swift,ahoppen/swift,sschiau/swift,gmilos/swift,cbrentharris/swift,ben-ng/swift,glessard/swift,therealbnut/swift,CodaFi/swift,danielmartin/swift,JGiola/swift,jckarter/swift,xedin/swift,emilstahl/swift,arvedviehweger/swift,jopamer/swift,parkera/swift,hughbe/swift,OscarSwanros/swift,devincoughlin/swift,gribozavr/swift,kstaring/swift,arvedviehweger/swift,mightydeveloper/swift,emilstahl/swift,calebd/swift,karwa/swift,apple/swift,atrick/swift,stephentyrone/swift,uasys/swift,tkremenek/swift,johnno1962d/swift,OscarSwanros/swift,tardieu/swift,LeoShimonaka/swift,benlangmuir/swift,tjw/swift,JaSpa/swift,nathawes/swift,glessard/swift,cbrentharris/swift,karwa/swift,hughbe/swift,danielmartin/swift,mightydeveloper/swift,JaSpa/swift,jmgc/swift,manavgabhawala/swift,Jnosh/swift,airspeedswift/swift,xedin/swift,mightydeveloper/swift,tardieu/swift,practicalswift/swift,LeoShimonaka/swift,manavgabhawala/swift,hooman/swift,frootloops/swift,lorentey/swift,glessard/swift,xwu/swift,nathawes/swift,ahoppen/swift,natecook1000/swift,natecook1000/swift,gregomni/swift,practicalswift/swift,sdulal/swift,swiftix/swift,huonw/swift,return/swift,ben-ng/swift,devincoughlin/swift,codestergit/swift,kusl/swift,parkera/swift,allevato/swift,KrishMunot/swift,tardieu/swift,CodaFi/swift,shahmishal/swift,ken0nek/swift,dreamsxin/swift,natecook1000/swift,kstaring/swift,jtbandes/swift,slavapestov/swift,lorentey/swift,felix91gr/swift,jopamer/swift,kperryua/swift,karwa/swift,ken0nek/swift,tjw/swift,apple/swift,swiftix/swift,CodaFi/swift,swiftix/swift.old,deyton/swift,uasys/swift,LeoShimonaka/swift,harlanhaskins/swift,SwiftAndroid/swift,parkera/swift,lorentey/swift,slavapestov/swift,ken0nek/swift,codestergit/swift,parkera/swift,amraboelela/swift,swiftix/swift.old,airspeedswift/swift,jopamer/swift,apple/swift,frootloops/swift,JGiola/swift,kstaring/swift,jopamer/swift,jtbandes/swift