Error: Unsupported map representation "stringpairs"

I was attempting to use the [stringpairs](https://ipld.io/docs/schemas/features/representation-strategies/#map-stringpairs-representation) representation for a schema, but got an error when trying to pass it to the `create()` function in `typed.js`.

Here's the schema I used:

```ipld-schema
type Example {String:String} representation stringpairs {
entryDelim ","
innerDelim " "
}
```

Did I do something wrong? It appears as though `typed.js` just doesn't support this functionality.