diff --git a/api/chalicelib/core/custom_metrics.py b/api/chalicelib/core/custom_metrics.py
index 236533b99..ab0b7d15f 100644
--- a/api/chalicelib/core/custom_metrics.py
+++ b/api/chalicelib/core/custom_metrics.py
@@ -107,6 +107,8 @@ def get_sessions(project_id, user_id, metric_id, data: schemas.CustomMetricSessi
 
 def try_sessions(project_id, user_id, data: schemas.CustomMetricSessionsPayloadSchema):
     results = []
+    if data.series is None:
+        return results
     for s in data.series:
         s.filter.startDate = data.startTimestamp
         s.filter.endDate = data.endTimestamp