Graphql studio getting null data - express

Question

I am new to Graphql, express, and Apollo.
Expected result: I am trying to consume data from JSON file data and get results in the studio.
Actual Result: Getting "null" data instead.
I am attaching my code snippets and problems below
Refer the following:
Let me show you the code:
directory structure:
MOCK_DATA.json
I am just keeping data small for testing the concept.
[{
"name": "Leanne Graham",
"username": "Bret"
},
{
"name": "Rohit Sharma",
"username": "rohituid"
}]
index.js
As per my understanding, The significance of the file is wiring up the express middle wire with the Apollo server. Tried to make this file in a way that it will be hardly touched.
Other than that, I have the async function was required to fix Apollo Server await server.start bug .
I am creating apollo server
const { ApolloServer } = require("apollo-server-express");
const { typeDefs } = require("./Schema/TypeDefs");
const { resolver } = require("./Schema/Resolver");
const express = require("express");
const app = express();
const PORT = 3001;
async function createApolloServer() {
//passing into apollo constructor
const server = new ApolloServer({
typeDefs,
resolver
});
//instantiatiating the apollo server
await server.start();
//this will install the apollo server on express app
server.applyMiddleware({ app });
}
createApolloServer();
//console.log(resolver);
app.listen(PORT, () => {
console.log('Server is running on : http://localhost:3001/graphql');
Schema:
TypeDefs.js
const { ApolloServer, gql } = require("apollo-server");
//below is known as tagged template literal
const typeDefs = gql`
type User {
name: String
username: String
}
#Queries -like get in REST World
type Query {
getAllUsers: [User]
}
`;
//console.log(typeDefs);
module.exports = { typeDefs };
Resolver.js
const userData = require("../MOCK_DATA.json");
//const userData = require("../FakeData.js");
// this is resolver map -> javascript object
//using arrow function
/*
below arrow function equivalent to using function like:
function getAllUsers() {
return userData;
}
*/
const resolver = {
Query: {
getAllUsers: ()=> {
return userData;
}
},
};
//console.log(userData);
module.exports = { resolver };