diff --git a/src/google/adk/evaluation/evaluation_generator.py b/src/google/adk/evaluation/evaluation_generator.py
index 1d9662bd..725bddc1 100644
--- a/src/google/adk/evaluation/evaluation_generator.py
+++ b/src/google/adk/evaluation/evaluation_generator.py
@@ -280,7 +280,7 @@ class EvaluationGenerator:
     invocations = []
     for invocation_id, events in events_by_invocation_id.items():
       final_response = None
-      user_content = ""
+      user_content = Content(parts=[])
       invocation_timestamp = 0
       app_details = None
       if (