Update app.py

Return None instead of empty list

app.py

@@ -25,16 +25,23 @@ class Run:
         self.outside_power = moon.outside_max_power
 
 
-def find_spawnlist(remaining_power: int, creatures: list[Creature]) -> list[str]:
+def find_spawnlist(remaining_power: int, creatures: list[Creature]) -> list[str] | None:
     """
     Given a run, return all possible spwns for location.
 
     :param remaining_power: The remaining power in the current location.
     :return: A list of all creatures that may still spawn.
     """
-    return sorted(
+    if remaining_power == 0:
+        return None
+
+    spawnable = sorted(
         [creature.name for creature in creatures if creature.power <= remaining_power]
     )
+    if spawnable != []:
+        return spawnable
+    else:
+        return None
 
 
 def main():