diff --git a/functions/classes.py b/functions/classes.py
index 00df6998df423f85de2d4a821f169381afcddbf9..7783406ee9bdefb0bcdc5df85d84a2b04c1c9181 100644
--- a/functions/classes.py
+++ b/functions/classes.py
@@ -254,3 +254,4 @@ class KPIEncoder(json.JSONEncoder):
             return "kpi-" + str(o)
         if isinstance(o, (AggregationLayer)):
             return "kpi-" + o.properties.label
+        return super().default(o)