Fix return nil (#15330)

* Fix return nil

A nil error is an interface having nil value but a non-nil type.
This leads to unexpected errors in the code well-documented here:
https://golang.org/doc/faq#nil_error

We fix this by passing an additional parameter to handle it.

Caught using https://github.com/dgryski/semgrep-go

* Bring back auto-generated line

config/file.go

@@ -234,7 +234,7 @@ func (fs *FileStore) RemoveFile(name string) error {
 		return errors.Wrap(err, "failed to remove file")
 	}
 
-	return err
+	return nil
 }
 
 // startWatcher starts a watcher to monitor for external config file changes.