Fix broken tests relevant to replacing null with undefined
Fix broken tests relevant to replacing null with undefined

jamiehodge/express-graphql,wincent/express-graphql,jamiehodge/express-graphql,wincent/express-graphql,wincent/express-graphql,graphql/express-graphql,jamiehodge/express-graphql,graphql/express-graphql,graphql/express-graphql