Unhandled Rejection (TypeError): Cannot read property 'error' of undefined

[aaron2181]

I keep getting the below error when trying to login. How do I fix it?

Unhandled Rejection (TypeError): Cannot read property 'error' of undefined
(anonymous function)
D:/CovidApp/Covid19nu/react-frontend/src/components/Login.js:29
26 | }
27 |
28 | login(user).then(res => {

29 | if (!res.error) {
| ^ 30 | this.props.history.push(/profile)
31 | }
32 | })