Doesn't work with ESM

[Trojaner]

Version

4.0.4

Reproduction link

https://plnkr.co/edit/0TYlxtktHJ1MszrL

Steps to reproduce

1. Open repro link
2. Observe error in console

What is expected?

App should show and not generate an error

What is actually happening?

vue.esm-browser.prod.js?module:1 TypeError: Cannot read property 'parent' of null
    at warnDeprecatedUsage (vue-router.esm.js?module:2152)
    at setup (vue-router.esm.js?module:2071)
    at kt (vue.esm-browser.prod.js?module:1)
    at vue.esm-browser.prod.js?module:1
    at vue.esm-browser.prod.js?module:1
    at B (vue.esm-browser.prod.js?module:1)
    at O (vue.esm-browser.prod.js?module:1)
    at b (vue.esm-browser.prod.js?module:1)
    at E (vue.esm-browser.prod.js?module:1)
    at T (vue.esm-browser.prod.js?module:1)

---

Tested with es-module-shims and Chrome's own ESM implementation, both resulted in the same error

[posva]

Not sure if you are referring to this: #694.

Otherwise, please read https://new-issue.vuejs.org/?repo=vuejs/vue#why-repro

[Trojaner]

This is a different issue and unrelated to #694. I will try to create an online repro, but you can also use the repo I have linked.

[Trojaner]

Here is the repro, please reopen the issue: https://plnkr.co/edit/0TYlxtktHJ1MszrL