fix(util): guard _datetime_from_weaviate_str against empty string

mock_tests/conftest.py

@@ -241,6 +241,40 @@ def Search(
     return weaviate_client.collections.use("YearZeroCollection")
 
 
+@pytest.fixture(scope="function")
+def empty_date_collection(
+    weaviate_client: weaviate.WeaviateClient, start_grpc_server: grpc.Server
+) -> weaviate.collections.Collection:
+    class MockWeaviateService(weaviate_pb2_grpc.WeaviateServicer):
+        def Search(
+            self, request: search_get_pb2.SearchRequest, context: grpc.ServicerContext
+        ) -> search_get_pb2.SearchReply:
+            # An empty date_value explicitly sets the oneof, so it passes the HasField guard;
+            # a repeated string has no per-element presence at all.
+            date_props: Mapping[str, properties_pb2.Value] = {
+                "date": properties_pb2.Value(date_value=""),
+                "dates": properties_pb2.Value(
+                    list_value=properties_pb2.ListValue(
+                        date_values=properties_pb2.DateValues(
+                            values=["", "2023-01-15T14:30:45.123456Z"]
+                        )
+                    )
+                ),
+            }
+            return search_get_pb2.SearchReply(
+                results=[
+                    search_get_pb2.SearchResult(
+                        properties=search_get_pb2.PropertiesResult(
+                            non_ref_props=properties_pb2.Properties(fields=date_props)
+                        )
+                    ),
+                ]
+            )
+
+    weaviate_pb2_grpc.add_WeaviateServicer_to_server(MockWeaviateService(), start_grpc_server)
+    return weaviate_client.collections.use("EmptyDateCollection")
+
+
 @pytest.fixture(scope="function")
 def timeouts_collection(
     weaviate_timeouts_client: weaviate.WeaviateClient, start_grpc_server: grpc.Server

mock_tests/test_collection.py

@@ -293,6 +293,18 @@ def test_year_zero(year_zero_collection: weaviate.collections.Collection) -> Non
         assert str(recwarn[0].message).startswith("Con004")
 
 
+def test_empty_date(empty_date_collection: weaviate.collections.Collection) -> None:
+    with pytest.warns(UserWarning) as recwarn:
+        objs = empty_date_collection.query.fetch_objects().objects
+        assert objs[0].properties["date"] is None
+        assert objs[0].properties["dates"] == [
+            None,
+            datetime.datetime(2023, 1, 15, 14, 30, 45, 123456, tzinfo=datetime.timezone.utc),
+        ]
+
+        assert str(recwarn[0].message).startswith("Con006")
+
+
 @pytest.mark.parametrize("output", ["minimal", "verbose"])
 def test_node_with_timeout(
     httpserver: HTTPServer, start_grpc_server: grpc.Server, output: Literal["minimal", "verbose"]

test/test_util.py

@@ -2,6 +2,7 @@
 import uuid as uuid_lib
 from copy import deepcopy
 from datetime import datetime, timedelta, timezone
+from typing import Optional
 from unittest.mock import Mock, patch
 
 import pytest
@@ -458,12 +459,19 @@ def test_is_weaviate_too_old(version: str, too_old: bool):
         ),
         # Test handling year 0 (should return datetime.min)
         ("0000-01-15T14:30:45.123456Z", datetime.min),
+        # Test empty string (protobuf default for unset string field) -> None
+        ("", None),
     ],
 )
-def test_datetime_from_weaviate_str(input_str: str, expected: datetime) -> None:
+def test_datetime_from_weaviate_str(input_str: str, expected: Optional[datetime]) -> None:
     assert _datetime_from_weaviate_str(input_str) == expected
 
 
+def test_datetime_from_weaviate_str_empty_string_warns() -> None:
+    with pytest.warns(UserWarning, match="Con006"):
+        assert _datetime_from_weaviate_str("") is None
+
+
 @pytest.mark.parametrize(
     "current_version,latest_version,too_old",
     [

weaviate/util.py

@@ -761,7 +761,12 @@ def _datetime_to_string(value: TIME) -> str:
     return value.isoformat(sep="T", timespec="microseconds")
 
 
-def _datetime_from_weaviate_str(string: str) -> datetime.datetime:
+def _datetime_from_weaviate_str(string: str) -> Optional[datetime.datetime]:
+    # An unset date property arrives as null_value, never as "", so an empty string here
+    # can only be a malformed value from the server. Warn rather than drop it silently.
+    if not string:
+        _Warnings.datetime_empty_string()
+        return None
     if string[-1] != "Z":
         string = "".join(string.rsplit(":", 1))
 

weaviate/warnings.py

@@ -282,6 +282,16 @@ def datetime_year_zero(date: str) -> None:
             stacklevel=1,
         )
 
+    @staticmethod
+    def datetime_empty_string() -> None:
+        warnings.warn(
+            message="""Con006: Received an empty date string from Weaviate. This indicates a malformed or corrupt
+            date value, as an unset property is returned as null and never reaches this path.
+            None will be returned.""",
+            category=UserWarning,
+            stacklevel=1,
+        )
+
     @staticmethod
     def batch_refresh_failed(err: str) -> None:
         warnings.warn(