is that really all there is???

The specification says that with transfer_type=4, to_stop_id and
from_stop_id are optional values. Google disagrees and will fail
the publishing pipeline, so state them explicitly for them.

this marks all transfers within the same block as transfer type 4,
i.e. passangers may simply stay seated inside the same vehicle and
do not actually have to get off.

This reverts commit cc0dead864efe761719f1e21f731b7d3453379fd.

until we have dates for these trips, having them is a foreign key
violation.

as suggested by the gtfs validator of MobilityData