diff --git a/src/ui/test/test.py b/src/ui/test/test.py
index c776717..daaa804 100755
--- a/src/ui/test/test.py
+++ b/src/ui/test/test.py
@@ -358,7 +358,9 @@ class Test(Widget):
 
     @staticmethod
     def labellify(v):
-        if not isinstance(v, str):
+        if v is None:
+            v = "-"
+        elif isinstance(v, float):
             v = f"{v:.1f}"
         return v