A1: guard None/empty args in distance_service coefficients

backend/services/distance_service.py

@@ -118,6 +118,8 @@ def get_terrain_coefficient(terrain: str) -> float:
     Returns:
         Terrain coefficient (0.0 - 1.0)
     """
+    if not terrain:
+        return 0.5
     terrain_lower = terrain.lower()
 
     terrain_map = {
@@ -155,6 +157,8 @@ def get_time_of_day_coefficient(time_of_day: str) -> float:
     Returns:
         Time coefficient (0.0 - 1.0)
     """
+    if not time_of_day:
+        return 1.0
     time_lower = time_of_day.lower()
 
     if 'ночь' in time_lower:
@@ -175,6 +179,8 @@ def get_weather_coefficient(weather: str) -> float:
     Returns:
         Weather coefficient (0.0 - 1.0)
     """
+    if not weather:
+        return 1.0
     weather_lower = weather.lower()
 
     if 'ливень' in weather_lower or 'сильный дождь' in weather_lower: