Bug[data.gtfs.utils]: Missing references in attributions collision

[tkchouaki]

The attributions collision object is missing a references entry.

ile-de-france/data/gtfs/utils.py

Line 258 in 7f73d12

{ "slot": "attributions", "identifier": "attribution_id" },

This can cause a KeyError Exception at

ile-de-france/data/gtfs/utils.py

Line 304 in 7f73d12

for ref_slot, ref_identifier in collision["references"]: