diff --git a/python/packages/core/agent_framework/_evaluation.py b/python/packages/core/agent_framework/_evaluation.py
index cac000ca0b2..ab71d84a15c 100644
--- a/python/packages/core/agent_framework/_evaluation.py
+++ b/python/packages/core/agent_framework/_evaluation.py
@@ -797,8 +797,7 @@ def convert_message(message: Message) -> list[dict[str, Any]]:
                     "tool_call_id": c.call_id or "",
                     "name": c.name or "",
                 }
-                if args:
-                    tc["arguments"] = args
+                tc["arguments"] = args if args is not None else {}
                 content_items.append(tc)
             elif c.type == "function_result":
                 result_val = c.result
diff --git a/python/packages/foundry/tests/test_foundry_evals.py b/python/packages/foundry/tests/test_foundry_evals.py
index 575a5976bbf..f2b015e04c4 100644
--- a/python/packages/foundry/tests/test_foundry_evals.py
+++ b/python/packages/foundry/tests/test_foundry_evals.py
@@ -153,6 +153,23 @@ def test_assistant_with_tool_call(self) -> None:
         assert tc["name"] == "get_weather"
         assert tc["arguments"] == {"location": "Seattle"}
 
+    def test_assistant_with_zero_argument_tool_call(self) -> None:
+        msg = Message(
+            "assistant",
+            [
+                Content.from_function_call(
+                    call_id="call_3",
+                    name="get_site_summary",
+                    arguments=None,
+                ),
+            ],
+        )
+        result = AgentEvalConverter.convert_message(msg)
+        tc = result[0]["content"][0]
+        assert tc["type"] == "tool_call"
+        assert "arguments" in tc
+        assert tc["arguments"] == {}
+
     def test_assistant_text_and_tool_call(self) -> None:
         msg = Message(
             "assistant",