Fix eval parameters omit null description

py/src/braintrust/parameters.py

@@ -424,19 +424,19 @@ def serialize_eval_parameters(parameters: EvalParameters) -> dict[str, Any]:
 
     for name, schema in parameters.items():
         if _is_prompt_parameter(schema):
-            prompt_parameter_data: dict[str, Any] = {
-                "type": "prompt",
-                "description": schema.get("description"),
-            }
+            prompt_parameter_data: dict[str, Any] = {"type": "prompt"}
+            prompt_description = schema.get("description")
+            if prompt_description is not None:
+                prompt_parameter_data["description"] = prompt_description
             prompt_default = schema.get("default")
             if prompt_default is not None:
                 prompt_parameter_data["default"] = _prompt_data_to_dict(prompt_default)
             result[name] = prompt_parameter_data
         elif _is_model_parameter(schema):
-            model_parameter_data: dict[str, Any] = {
-                "type": "model",
-                "description": schema.get("description"),
-            }
+            model_parameter_data: dict[str, Any] = {"type": "model"}
+            model_description = schema.get("description")
+            if model_description is not None:
+                model_parameter_data["description"] = model_description
             model_default = schema.get("default")
             if model_default is not None:
                 model_parameter_data["default"] = model_default
@@ -451,8 +451,10 @@ def serialize_eval_parameters(parameters: EvalParameters) -> dict[str, Any]:
             data_parameter_data: dict[str, Any] = {
                 "type": "data",
                 "schema": schema_json,
-                "description": schema_json.get("description"),
             }
+            data_description = schema_json.get("description")
+            if data_description is not None:
+                data_parameter_data["description"] = data_description
             if "default" in schema_json:
                 data_parameter_data["default"] = schema_json["default"]
             result[name] = data_parameter_data

py/src/braintrust/test_parameters.py

@@ -635,3 +635,26 @@ def test_prompt_parameter_defaults_omit_none_values_from_dict():
     assert "function_call" not in default["prompt"]["messages"][0]
     assert "tool_calls" not in default["prompt"]["messages"][0]
     _assert_no_none_values(default)
+
+
+@pytest.mark.skipif(not HAS_PYDANTIC, reason="pydantic not installed")
+def test_serialize_eval_parameters_omits_description_when_absent():
+    from pydantic import BaseModel
+
+    class TemplateParam(BaseModel):
+        value: str = "default template"
+
+    serialized = serialize_eval_parameters(
+        {
+            "template": TemplateParam,
+            "main": {"type": "prompt"},
+            "judge_model": {"type": "model"},
+        }
+    )
+
+    assert serialized["template"]["type"] == "data"
+    assert serialized["template"]["default"] == "default template"
+    assert serialized["main"]["type"] == "prompt"
+    assert serialized["judge_model"]["type"] == "model"
+    for name in ("template", "main", "judge_model"):
+        assert "description" not in serialized[name]