In `Contacts.ts`, in the body of the `listContacts()` function, line 51 has: `(inError: Error, inDocs: IContact[]) => { ... ` This gives me an error, because this.db.find seems to expect the inError to be a union of Error and null. For the error to disappear, I had to change my code to this: `(inError: Error | null, inDocs: IContact[]) => { ... `