Upgrading from createContainer to withTracker with React Router V4 - meteor

Question

I upgraded meteor and I started receiving deprecation warning for createContainer(). As a result, I've tried to implement withTracker however now I'm getting Component(...): A valid React element (or null) must be returned. You may have returned undefined, an array or some other invalid object.. I'm not sure what I'm missing here, can someone point out my error.
Path: App.jsx
import { Meteor } from 'meteor/meteor';
import React from 'react';
import PropTypes from 'prop-types';
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import { withTracker } from 'meteor/react-meteor-data';
// IsCandidate Spefic Routes
import TestContainer from '../../containers/candidate/TestContainer';
const App = appProps => (
<Router>
<ScrollToTop>
<div className="bgColor">
<NavBar {...appProps} />
<Grid className="main-page-container">
<Switch>
{/* candidate routes */}
<IsCandidate exact path="/candidate/testpage/:id" component={withTracker(TestContainer)} {...appProps} />
{/* IsPublic routes */}
<Route render={function () {
return <p>Page not found</p>;
}}
/>
</Switch>
</Grid>
</div>
</ScrollToTop>
</Router>
);
App.propTypes = {
loggingIn: PropTypes.bool,
isCandidate: PropTypes.bool
};
export default createContainer(() => {
const loggingIn = Meteor.loggingIn();
return {
loggingIn,
isCandidate: !loggingIn && !!Meteor.userId() && !!Roles.userIsInRole(Meteor.userId(), 'isCandidate'),
};
}, App);
Path: IsCandidate.jsx
import React from 'react';
import PropTypes from 'prop-types'; // ES6
import { Route, Redirect } from 'react-router-dom';
const IsCandidate = ({ loggingIn, isCandidate, component: Component, ...rest }) => (
<Route
{...rest}
render={(props) => {
if (loggingIn) return <div />;
return isCandidate ?
(<Component loggingIn={loggingIn} isCandidate={isCandidate} {...rest} {...props} />) :
(<Redirect to="/login" />);
}}
/>
);
IsCandidate.propTypes = {
loggingIn: PropTypes.bool,
isCandidate: PropTypes.bool,
component: PropTypes.func
};
export default IsCandidate;
Path: Testcontainer.jsx
import { Meteor } from 'meteor/meteor';
import { withTracker } from 'meteor/react-meteor-data';
import { Test } from '../../../api/test/test';
import TestPage from '../../pages/candidate/TestPage';
export default TestContainer = withTracker(({ match }) => {
const testHandle = Meteor.subscribe('test', match.params.id);
const loadingTest = !testHandle.ready();
const testCollection = Test.findOne(match.params.id);
const testExist = !loadingTest && !!testCollection;
return {
loadingTest,
testExist,
testCollection: testExist ? testCollection : {}
};
}, TestPage);
Update
export default withTracker(() => {
const loggingIn = Meteor.loggingIn();
return {
loggingIn,
isCandidate: !loggingIn && !!Meteor.userId() && !!Roles.userIsInRole(Meteor.userId(), 'isCandidate'),
isEmployer: !loggingIn && !!Meteor.userId() && !!Roles.userIsInRole(Meteor.userId(), 'isEmployer'),
isAdmin: !loggingIn && !!Meteor.userId() && !!Roles.userIsInRole(Meteor.userId(), 'isAdmin')
};
})(App);

Answer 1

In App.jsx you import withTracker but use createContainer.
withTracker takes only one argument (your reactive function) and wraps your child component where createContainer took 2 arguments (function and component).
createContainer(fn, C);
withTracker(fn)(C);
EDIT
Remove the withTracker call in App.js from this line:
<IsCandidate exact path="/candidate/testpage/:id" component={withTracker(TestContainer)} {...appProps} />
so it becomes
<IsCandidate exact path="/candidate/testpage/:id" component={TestContainer} {...appProps} />
How about it?