Discussion on: Notes on TypeScript: Inferring React PropTypes

Type 'string | null | undefined' is not assignable to type 'string | undefined'

<div className={className}
                  ~~~~~~~~~

  node_modules/@types/react/index.d.ts:1645:9
    1645         className?: string;

const defaultProps = {
    className: 'user'
};
const propTypes = {
    className: PropTypes.string,
};

class User extends React.Component<UserProps> {
    static defaultProps = defaultProps;
    static propTypes: {};

    render() {
        let {className} = this.props;
        return (
            <div className={className}>test</div>
        );
    }
}
User.propTypes = propTypes;