Trivial s/NULL/nullptr

Author: swolchok

GraphQLParser.cpp

@@ -19,7 +19,7 @@ namespace graphql {
 // Given properly-configured yylex, run the parser and return the
 // result.
 static std::unique_ptr<ast::Node> doParse(const char **outError, yyscan_t scanner, bool enableSchema) {
-  Node *outAST = NULL;
+  Node *outAST = nullptr;
   yy::GraphQLParserImpl parser(enableSchema, &outAST, outError, scanner);
   int failure = parser.parse();
   if (failure) {