How to use the vue-class-component.default function in vue-class-component

import Vue from 'vue';
import { Store } from 'vuex';
import { State } from 'vuex-class';
import { default as Component } from 'vue-class-component';
import { IVuelidate, ValidationRuleset, Vuelidate, validationMixin } from 'vuelidate';
import { ICommonOptions } from '../../plugins';
import { AuthenticationService } from '../../services';
import { ISignupOptions, IUser } from '../../model';
import { IRouterMixinData } from '../../mixins/mixin-router';
import { ICommonState, StoreTypes } from '../../store';
import { validations, TSignup } from './signup-validate';

@Component({
    mixins: [validationMixin],
    name: 'Signup',
    template: require('./signup.html'),
    validations: validations
})
export class Signup extends Vue {

    private auth: AuthenticationService;

    @State((state: {common:ICommonState}) => state.common.user) user: IUser;

    constructor() {
        super();
    }

    created() {