I have recently stumbled across some valid Fedora n-v-r's that fedpkg gitbuildhash doesn't handle.
fedpkg gitbuildhash
$ fedpkg gitbuildhash mpich-3.2.1-2.fc27 Could not execute gitbuildhash: Unhandled build source git+https://src.fedoraproject.org/rpms/mpich.git?#8f5f8ca566fa01d2dcabc23cce373fb8cc76ec4e $ fedpkg gitbuildhash samba-4.7.1-0.fc28.1 Could not execute gitbuildhash: Unhandled build source git+https://src.fedoraproject.org/rpms/samba.git?#b6212110291cbc3c5de712c8b3c64516ada9b820 $
This can be fixed at rpkg level: rpkg#268
Metadata Update from @cqi: - Issue close_status updated to: Fixed - Issue status updated to: Closed (was: Open)