Use defaultdict, not Counter for travel distances

agenda/types.py

@@ -3,7 +3,7 @@
 import collections
 import datetime
 import typing
-from collections import Counter
+from collections import defaultdict
 from dataclasses import dataclass, field
 
 import emoji
@@ -190,12 +190,12 @@ class Trip:
 
         Any travel item with a missing or None 'distance' field is ignored.
         """
-        transport_distances: Counter[float] = Counter()
+        transport_distances: defaultdict[str, float] = defaultdict(float)
 
         for item in self.travel:
             distance = item.get("distance")
             if distance:
-                transport_type = item.get("type", "unknown")
+                transport_type: str = item.get("type", "unknown")
                 transport_distances[transport_type] += distance
 
         return list(transport_distances.items())