add a new isNull() method to DeclGroupRef.

llvm-svn: 68909
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index d2e1586..1428c48 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -40,10 +40,11 @@
 Sema::OwningStmtResult Sema::ActOnDeclStmt(DeclGroupPtrTy dg,
                                            SourceLocation StartLoc,
                                            SourceLocation EndLoc) {
-  // If we have an invalid decl, just return an error.
-  if (!dg) return StmtError();
-  
   DeclGroupRef DG = dg.getAsVal<DeclGroupRef>();
+  
+  // If we have an invalid decl, just return an error.
+  if (DG.isNull()) return StmtError();
+  
   return Owned(new (Context) DeclStmt(DG, StartLoc, EndLoc));
 }