react mobx - store return Proxy object

I have the following state class:

import { observable, action } from 'mobx';
import axios from 'axios';

export default class AppState {
  @observable user;
  @observable pToken;

  constructor() {
    this.user = {};
    this.pToken = localStorage.getItem('pToken');
  }

  async fetchData(query) {

    const body = JSON.stringify({ query, });
    const response = await axios.post('url', body, {
      headers: {
        'Content-Type': 'application/json',
        token: localStorage.getItem('pToken')
      }
    });

    const user = response.data.data.user;
    console.log('Got user', user);
    this.setUser(user);
  }

  @action setUser(user) {
    this.user = user;
  }
}

and in my component:

@inject('store')
@observer
export default class Header extends Component {
    constructor(props) {
        super(props);
        this.store = this.props.store.appState;
    }

    render() {
        const { user } = this.store;
        console.log('store', this.store);

        return (
            <header className='header'>
                User - {user.username}
            </header>
        );
    }
}

Unfortunately, the state user property returns a Proxy object, while the user log shows the user object. Any idea what I'm missing?