Error: Missing converter for X

This is a common issue with extract-react-types (ERT), which essentially means that:

**You are using a language feature that ERT is not familiar with**

> The way ERT evaluates complex types and language specific features is largely a manual process. We have to manually tell ERT how to interpret things like extends and React.FC, so inevitably there will be things that we don't support or haven't considered.

For a list of all supported and unsupported features, see this issue: https://github.com/atlassian/extract-react-types/issues/149

For example purposes, consider the scenario that the `unknown` keyword is not known to ERT. When the code below is parsed, it will error stating: `Missing converter for: TSUnknownKeyword `

```jsx
interface FooProps {
// Docs about the bar property here
bar: unknown;
}

const Foo = props => null;
```

If you are experiencing this issue, please leave a comment below or consider raising a pull request.