Error: There can be only one type named "RootQuery...?"

I'm getting this error and I don't know how to fix it.

I'm using GraphQL with a React front end. Everything is looking good, but on the back end I'm getting this:

C:\wamp64\www\adm\node\api\node_modules\graphql\validation\validate.js:108
    throw new Error(errors.map(function (error) {
    ^

Error: There can be only one type named "RootQuery".
    at assertValidSDL (C:\wamp64\www\adm\node\api\node_modules\graphql\validation\validate.js:108:11)
    at buildASTSchema (C:\wamp64\www\adm\node\api\node_modules\graphql\utilities\buildASTSchema.js:71:34)
    at buildSchema (C:\wamp64\www\adm\node\api\node_modules\graphql\utilities\buildASTSchema.js:462:10)
    at Object.<anonymous> (C:\wamp64\www\adm\node\api\graphql\schema.js:3:18)
    at Module._compile (internal/modules/cjs/loader.js:959:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:995:10)
    at Module.load (internal/modules/cjs/loader.js:815:32)
    at Function.Module._load (internal/modules/cjs/loader.js:727:14)
    at Module.require (internal/modules/cjs/loader.js:852:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (C:\wamp64\www\adm\node\api\app.js:9:23)
    at Module._compile (internal/modules/cjs/loader.js:959:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:995:10)
    at Module.load (internal/modules/cjs/loader.js:815:32)
    at Function.Module._load (internal/modules/cjs/loader.js:727:14)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1047:10)
[nodemon] app crashed - waiting for file changes before starting...

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I went out to the page that's being reference in the error and, first thing, it's part of a package, so I'm not going to be adjusting the syntax, so, I'm not sure what to think.

Here's the "validate.js" file:

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.validate = validate;
exports.validateSDL = validateSDL;
exports.assertValidSDL = assertValidSDL;
exports.assertValidSDLExtension = assertValidSDLExtension;
exports.ABORT_VALIDATION = void 0;

var _devAssert = _interopRequireDefault(require("../jsutils/devAssert"));

var _GraphQLError = require("../error/GraphQLError");

var _visitor = require("../language/visitor");

var _validate = require("../type/validate");

var _TypeInfo = require("../utilities/TypeInfo");

var _specifiedRules = require("./specifiedRules");

var _ValidationContext = require("./ValidationContext");

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

var ABORT_VALIDATION = Object.freeze({});
/**
 * Implements the "Validation" section of the spec.
 *
 * Validation runs synchronously, returning an array of encountered errors, or
 * an empty array if no errors were encountered and the document is valid.
 *
 * A list of specific validation rules may be provided. If not provided, the
 * default list of rules defined by the GraphQL specification will be used.
 *
 * Each validation rules is a function which returns a visitor
 * (see the language/visitor API). Visitor methods are expected to return
 * GraphQLErrors, or Arrays of GraphQLErrors when invalid.
 *
 * Optionally a custom TypeInfo instance may be provided. If not provided, one
 * will be created from the provided schema.
 */

exports.ABORT_VALIDATION = ABORT_VALIDATION;

function validate(schema, documentAST) {
  var rules = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : _specifiedRules.specifiedRules;
  var typeInfo = arguments.length > 3 && arguments[3] !== undefined ? arguments[3] : new _TypeInfo.TypeInfo(schema);
  var options = arguments.length > 4 ? arguments[4] : undefined;
  documentAST || (0, _devAssert.default)(0, 'Must provide document'); // If the schema used for validation is invalid, throw an error.

  (0, _validate.assertValidSchema)(schema);
  var abortObj = Object.freeze({});
  var errors = [];
  var maxErrors = options && options.maxErrors;
  var context = new _ValidationContext.ValidationContext(schema, documentAST, typeInfo, function (error) {
    if (maxErrors != null && errors.length >= maxErrors) {
      errors.push(new _GraphQLError.GraphQLError('Too many validation errors, error limit reached. Validation aborted.'));
      throw abortObj;
    }

    errors.push(error);
  }); // This uses a specialized visitor which runs multiple visitors in parallel,
  // while maintaining the visitor skip and break API.

  var visitor = (0, _visitor.visitInParallel)(rules.map(function (rule) {
    return rule(context);
  })); // Visit the whole document with each instance of all provided rules.

  try {
    (0, _visitor.visit)(documentAST, (0, _visitor.visitWithTypeInfo)(typeInfo, visitor));
  } catch (e) {
    if (e !== abortObj) {
      throw e;
    }
  }

  return errors;
} // @internal


function validateSDL(documentAST, schemaToExtend) {
  var rules = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : _specifiedRules.specifiedSDLRules;
  var errors = [];
  var context = new _ValidationContext.SDLValidationContext(documentAST, schemaToExtend, function (error) {
    errors.push(error);
  });
  var visitors = rules.map(function (rule) {
    return rule(context);
  });
  (0, _visitor.visit)(documentAST, (0, _visitor.visitInParallel)(visitors));
  return errors;
}
/**
 * Utility function which asserts a SDL document is valid by throwing an error
 * if it is invalid.
 *
 * @internal
 */


function assertValidSDL(documentAST) {
  var errors = validateSDL(documentAST);

  if (errors.length !== 0) {
    throw new Error(errors.map(function (error) {
      return error.message;
    }).join('\n\n'));
  }
}
/**
 * Utility function which asserts a SDL document is valid by throwing an error
 * if it is invalid.
 *
 * @internal
 */


function assertValidSDLExtension(documentAST, schema) {
  var errors = validateSDL(documentAST, schema);

  if (errors.length !== 0) {
    throw new Error(errors.map(function (error) {
      return error.message;
    }).join('\n\n'));
  }
}

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What's the problem and how do I fix it?