Removed multiple return types.

sport_activities_features/training_metrics.py

@@ -103,7 +103,7 @@ def prepare_normalized_power_data(self,tcx: TCXExercise, window_size:float = 30,
 
         return power_data
 
-    def normalized_power(self, power_data: list, window_size: int) -> float|None:        
+    def normalized_power(self, power_data: list, window_size: int) -> float:
         """Method for calculating normalized power (NP).\n
         Args:
             power_data (list):