Add instance check for reward function

Current reward function assumes a single detection per track
This adds an instance check to manage clutter.

stonesoup/sensormanager/reward.py

@@ -5,6 +5,7 @@
 
 import numpy as np
 
+from stonesoup.types.detection import TrueDetection
 from ..base import Base, Property
 from ..predictor.kalman import KalmanPredictor
 from ..updater.kalman import ExtendedKalmanUpdater
@@ -102,7 +103,8 @@ def __call__(self, config: Mapping[Sensor, Sequence[Action]], tracks: Set[Track]
 
             # Assumes one detection per track
             detections = {detection.groundtruth_path: detection
-                          for detection in sensor.measure(predicted_tracks, noise=False)}
+                          for detection in sensor.measure(predicted_tracks, noise=False)
+                          if isinstance(detection, TrueDetection)}
 
             for predicted_track, detection in detections.items():
                 # Generate hypothesis based on prediction/previous update and detection