How to update upstream when upstream has no releases

[Tong Sun <suntong001@users.sourceforge.net>]

Hi,

How to use `gbp import-orig` to update upstream when upstream has no releases?

I was using `gbp import-orig --sign-tags --uscan` but it seems that
`--uscan` cannot be used with `gbp import-orig` under the case of no
upstream releases.

I'm using the Dep14 Workflow so no pristine tar branch needed.

Thanks