[trackingdata] scores returns None, if no detections in range

fixtracks/utils/trackingdata.py

@@ -169,11 +169,11 @@ class TrackingData(QObject):
         numpy.ndarray
             A NumPy array of type float32 containing the keypoint scores of the shape (N, M) 
             with N the number of detections and M the number of keypoints.
-        """ 
+        """
         if selection:
             if len(self._indices) < 1:
                 logging.info("TrackingData.scores returns empty array, not detections in range!")
-                return np.ndarray([])
+                return None
             return np.stack(self._data["keypoint_score"][self._indices]).astype(np.float32)
         return np.stack(self._data["keypoint_score"]).astype(np.float32)
 
@@ -195,6 +195,8 @@ class TrackingData(QObject):
         A NumPy array of shape (N, 2) containing the center of gravity for each detection.
         """
         scores = self.keypointScores(selection)
+        if scores is None:
+            return None
         scores[scores < threshold] = 0.0
         scores[:, np.setdiff1d(np.arange(scores.shape[1]), nodes)] = 0.0
         weighted_coords = self.coordinates(selection=selection) * scores[:, :, np.newaxis]