diff --git a/motpy/core.py b/motpy/core.py
index e06fd61..fafa5c8 100644
--- a/motpy/core.py
+++ b/motpy/core.py
@@ -35,7 +35,7 @@ def __init__(
         self.feature = feature
 
     def __repr__(self):
-        return f'Detection(box={self.box}, score={self.score:.5f}, class_id={self.class_id}, feature={self.feature})'
+        return f'Detection(box={self.box}, score={f"{self.score:.5f}" if self.score else None}, class_id={self.class_id}, feature={self.feature})'
 
 
 """ utils """
diff --git a/motpy/tracker.py b/motpy/tracker.py
index d5eb9fd..8f8efde 100644
--- a/motpy/tracker.py
+++ b/motpy/tracker.py
@@ -374,7 +374,7 @@ def active_tracks(self,
             if cond1 and cond2 and cond3:
                 tracks.append(Track(id=tracker.id, box=tracker.box(), score=tracker.score, class_id=tracker.class_id))
 
-        logger.debug('active/all tracks: %d/%d' % (len(self.trackers), len(tracks)))
+        logger.debug(f'active/all tracks: {len(tracks)}/{len(self.trackers)}')
         return tracks
 
     def cleanup_trackers(self) -> None: