fix(sagemaker-core): preserve falsy values in serialize() output (#5860)

The walrus check in _serialize_dict and _serialize_list silently dropped
False / 0 / "" along with None / Unassigned, because all of them are
falsy. Boolean parameters that should reach the wire as False were
instead omitted, causing the server to apply its own default (often
True), which led to confusing validation errors that contradicted the
caller's input.

Concrete failure: AIRecommendationJob.create(optimize_model=False)
silently sent OptimizeModel=True, then failed with a server message
about a missing DatasetConfig — a requirement that only applies when
OptimizeModel is True.

Replace the walrus truthy guard with an explicit `is not None` check.
serialize() already returns None for both None and Unassigned (utils.py
line 512), so this preserves the "drop unset fields" semantics while
correctly retaining valid falsy payloads.

Adds two regression tests covering False / 0 / "" preservation and
None / Unassigned removal.

Author: ZealSV

sagemaker-core/src/sagemaker/core/utils/utils.py

@@ -538,9 +538,11 @@ def _serialize_dict(value: Dict) -> dict:
         dict: The serialized dict
     """
     serialized_dict = {}
+    # Drop only Unassigned/None; preserve valid falsy values like False, 0, "".
     for k, v in value.items():
-        if serialize_result := serialize(v):
-            serialized_dict.update({k: serialize_result})
+        serialize_result = serialize(v)
+        if serialize_result is not None:
+            serialized_dict[k] = serialize_result
     return serialized_dict
 
 
@@ -555,8 +557,10 @@ def _serialize_list(value: List) -> list:
         list: The serialized list
     """
     serialized_list = []
+    # Drop only Unassigned/None; preserve valid falsy values like False, 0, "".
     for v in value:
-        if serialize_result := serialize(v):
+        serialize_result = serialize(v)
+        if serialize_result is not None:
             serialized_list.append(serialize_result)
     return serialized_list
 

sagemaker-core/tests/unit/generated/test_utils.py

@@ -353,6 +353,20 @@ def test_serialize_method_returns_correct_data():
     assert serialized_data["S3Uri"] == "s3/uri"
 
 
+def test_serialize_preserves_falsy_dict_values():
+    # Regression: previously False / 0 / "" were stripped along with None.
+    assert serialize({"k": False}) == {"k": False}
+    assert serialize({"k": 0}) == {"k": 0}
+    assert serialize({"k": ""}) == {"k": ""}
+    assert serialize({"k": None}) == {}
+    assert serialize({"k": Unassigned()}) == {}
+
+
+def test_serialize_preserves_falsy_list_values():
+    assert serialize([False, 0, ""]) == [False, 0, ""]
+    assert serialize([None, "x", Unassigned(), 1]) == ["x", 1]
+
+
 def test_serialize_method_nested_shape():
     trial_component_parameters = {
         "test_num_value": TrialComponentParameterValue(number_value=1),