Add check for decl nullptr to ASTNodeTraverser::Visit

Author: JonathanMarriott

clang/include/clang/AST/ASTNodeTraverser.h

@@ -99,7 +99,7 @@ class ASTNodeTraverser
   TraversalKind GetTraversalKind() const { return Traversal; }
 
   void Visit(const Decl *D, bool VisitLocs = false) {
-    if (Traversal == TK_IgnoreUnlessSpelledInSource && D->isImplicit())
+    if (Traversal == TK_IgnoreUnlessSpelledInSource && D && D->isImplicit())
       return;
 
     getNodeDelegate().AddChild([=] {