**What**
- Provide a more helpful error message if a user adds a file in `src/services` that doesn't export a service class.
**Why**
If you forget to `export default MyClass` in a custom service you can end up with this error:
It's almost impossible to know how to recover from this which can be an issue for new users. The new error message informs the user that there is a missing class export and shows which file the error is related to.
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