GraphQLError [Object]: Syntax Error: Expected ":", found Name "User". in express-graphql

Question

I am trying to create a user using createUser mutation in express.js using express-graphql. But as I try to run the code using npm start I get the following error: GraphQLError [Object]: Syntax Error: Expected ":", found Name "User". My schema is:

const { buildSchema } = require("graphql");

module.exports = buildSchema(`

  type Option {
    value: String!
    text: String!
    key: String!
    correct: Boolean
  }

  type FormData {
    id: ID!
    required: Boolean!
    element: String!
    text: String!
    canHavePageBreakBefore: Boolean!
    canHaveAlternateForm: Boolean!
    canHaveDisplayHorizontal: Boolean!
    canHaveOptionCorrect: Boolean!
    canHaveOptionValue: Boolean!
    canPopulateFromApi: Boolean!
    canHaveAnswer: Boolean
    href: String
    src: String
    dateFormat: String
    timeFormat: String
    showTimeSelect: Boolean
    showTimeSelectOnly: Boolean
    _href: String
    file_path: String
    step: Int
    default_value: Int
    min_value: Int
    max_value: Int
    min_label: String
    max_label: String
    field_name: String
    label: String
    dirty: Boolean
    options: [Option!]
  }

  type Form {
    _id: ID!
    title: String!
    creator: User!
    description: String!
    formData: [FormData!]
    createdAt: String!
    updatedAt: String!
  
  type User {
    _id: ID!
    name: String!
    email: String!
    password: String
    college: String
    createdForms: [Form!]
    bookmarks: [Form!]
    dob: String
    imageUrl: String
  }

  input UserInputData {
    name: String!
    email: String!
    password: String!
    college: String!
  }

  type RootMutation {
    createUser(userInput: UserInputData): User!
  }

  schema {
    mutation: RootMutation
  }

`);

My resolver function is:

const User = require("../models/user");
const bcrypt = require("bcryptjs");

module.exports = {
  createUser: async function ({ userInput }, req) {
    const existingUser = await User.findOne({ email: userInput.email });
    if (existingUser) {
      const error = new Error("User exists already.");
      throw error;
    }
    const hashedPassword = await bcrypt.hash(userInput.password, 12);
    const user = new User({
      name: userInput.name,
      email: userInput.email,
      password: hashedPassword,
      college: userInput.college,
    });
    const createdUser = await user.save();
    return { ...createdUser._doc, _id: createdUser._id.toString() };
  },
};

The complete error is:

C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:1413
    throw (0, _syntaxError.syntaxError)(this._lexer.source, token.start, "Expected ".concat(getTokenKindDesc(kind), ", found ").concat(getTokenDesc(token), "."));
    ^

GraphQLError [Object]: Syntax Error: Expected ":", found Name "User".
    at syntaxError (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\error\syntaxError.js:15:10)
    at Parser.expectToken (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:1413:40)
    at Parser.parseFieldDefinition (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:881:10)
    at Parser.optionalMany (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:1503:28)
    at Parser.parseFieldsDefinition (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:868:17)
    at Parser.parseObjectTypeDefinition (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:812:23)       
    at Parser.parseTypeSystemDefinition (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:708:23)
    at Parser.parseDefinition (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:150:23)
    at Parser.many (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:1523:26)
    at Parser.parseDocument (C:\Users\Asus\Desktop\Project A\project-g\node_modules\graphql\language\parser.js:115:25) {
  locations: [ { line: 51, column: 8 } ]
}

Can anyone please help me out? I can't figure it out. Thanks.