Fix -Wsentinel warning

llvm-svn: 297560
diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index 8b95058..a3ca276 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -1252,7 +1252,7 @@
   // Create the function using an IR-level function.
   LLVMContext &C = M.getContext();
   Function *F = dyn_cast<Function>(
-      M.getOrInsertFunction(NameStream.str(), Type::getVoidTy(C), NULL));
+      M.getOrInsertFunction(NameStream.str(), Type::getVoidTy(C), nullptr));
   assert(F && "Function was null!");
 
   // NOTE: If this is linkonceodr, then we can take advantage of linker deduping