Uncaught TypeError: get(...) is not a function

Running into an issue here where the following error is being thrown:

```
Uncaught TypeError: get(...) is not a function
at Class. (stripe-element.js:23)
```

Looks like `get(this, "stripev3.elements")` is returning undefined, so calling that function is blowing up. Any idea why this might be happening?

Start at stripe-element.js:23 and trace where get(this, "stripev3.elements") is initialized and where the failing call is reached. Reproduce the reported TypeError and verify that the relevant Stripe Elements value is available before it is invoked; no test or additional file is named in the issue.

索引モデルが issue の本文から書いたものです。