Return 400 if references missing from cancel broadcast

If someone tries to cancel a broadcast but the references don’t match
and existing broadcast we correctly return a 404.

If they don’t provide any references then we get an exception. This
commit catches the missing references and returns a 400. I think this
is more appropriate because it’s malformed request, rather than a
well-formed request that doesn’t match our data. It also lets us write a
more specific and helpful error message.

app/broadcast_message/translators.py

@@ -7,7 +7,10 @@ def cap_xml_to_dict(cap_xml):
     return {
         "msgType": cap.alert.msgType.text,
         "reference": cap.alert.identifier.text,
-        "references": cap.alert.references.text,  # references to previous events belonging to the same alert
+        "references": (
+            # references to previous events belonging to the same alert
+            cap.alert.references.text if cap.alert.references else None
+        ),
         "cap_event": cap.alert.info.event.text,
         "category": cap.alert.info.category.text,
         "expires": cap.alert.info.expires.text,

app/v2/broadcast/post_broadcast.py

@@ -48,6 +48,11 @@ def create_broadcast():
     validate(broadcast_json, post_broadcast_schema)
 
     if broadcast_json["msgType"] == "Cancel":
+        if broadcast_json["references"] is None:
+            raise BadRequestError(
+                message='Missing <references>',
+                status_code=400,
+            )
         broadcast_message = _cancel_or_reject_broadcast(
             broadcast_json["references"].split(","),
             authenticated_service.id