expected value of type undefined during 'init', but received: [object Object]

I'm using mirage for testing, and I have type validation on one of my models. When I run a test, I'm seeing this:

`_default#proposedGeometry expected value of type undefined during 'init', but received: [object Object]`

But I _have_ defined the type as something:

```javascript
import { FeatureCollection, EmptyFeatureCollection } from './project';

// ... class {

@type(FeatureCollection)
@attr({ defaultValue: () => EmptyFeatureCollection })
proposedGeometry;
```

The problem is that FeatureCollection actually imports as `undefined` in my test environment. Could this have something to do with e-decorators stripping out type validation in the wrong place?