diff --git a/src/humanloop/eval_utils.py b/src/humanloop/eval_utils.py
index 1eb09e2f..1e003e97 100644
--- a/src/humanloop/eval_utils.py
+++ b/src/humanloop/eval_utils.py
@@ -325,7 +325,7 @@ def process_datapoint(datapoint: Datapoint):
         start_time = datetime.now()
         datapoint_dict = datapoint.dict()
         try:
-            if "messages" in datapoint_dict:
+            if "messages" in datapoint_dict and datapoint_dict["messages"] is not None:
                 output = function_(
                     **datapoint_dict["inputs"], messages=datapoint_dict["messages"]
                 )