Getting a "TransformError: Unexpected token ," from a Flow type

Can anyone help me understand why this isn't working?

```
type RemoveFromBagParams = {bag: mixed, addedItemsBin: string, removedItemsBin: string, itemToBeRemoved: Array<string> };
```

It errors out with 

```
SyntaxError: TransformError: Unexpected token ,
```

I'm using React Native version 0.4.0 with Flow version 0.9.2.
