fix issue with court name

tournaments/models/club.py

@@ -28,4 +28,8 @@ class Club(models.Model):
         for court in self.court_set.all():
             if court.index == index and court.name is not None and len(court.name) > 0:
                 return court.name
-        return f"Terrain {index + 1}"
+
+        if index is not None:
+            return f"Terrain {index + 1}"
+
+        return ""