Do not construct StringRef from NULL argument.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@163465 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 1d5ee0c..8bb5a2d 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -3014,7 +3014,7 @@
     return llvm::StringSwitch<const char*>(Name)
       .Cases("cortex-a8", "cortex-a9", "A")
       .Cases("cortex-m3", "cortex-m4", "cortex-m0", "M")
-      .Default(0);
+      .Default("");
   }
   virtual bool setCPU(const std::string &Name) {
     if (!getCPUDefineSuffix(Name))