It is kind of pointless to let the tool run if no source data is
present, so treat empty/missing source as an error.
Signed-off-by: John Mulligan <jmulligan@redhat.com>
This tool can be run as part of our CI as a mechanism to check that
(some) of the policy requirements are being met. It can also be run by
humans as part of the process to update the tracked API information.
Signed-off-by: John Mulligan <jmulligan@redhat.com>