Python: Keep null fields out of Azure DocumentDB membership filters

python/packages/azure-documentdb/agent_framework_azure_documentdb/_vector_store.py

@@ -429,19 +429,16 @@ def _prepare_filter_condition(self, expression: FilterExpression) -> _Document:
                 raise NotImplementedError(
                     "Use contains, contains_any, or contains_all for Azure DocumentDB list fields."
                 )
-            operands = [_prepare_filter_operand(field, item) for item in value]
+            # Portable membership, unlike eq/ne, never matches a null field, even when None is an operand.
+            operands = [_prepare_filter_operand(field, item) for item in value if item is not None]
             operands = [item for item in operands if item is not _TYPE_MISMATCH]
             if not operands:
                 if operator == "in":
                     return self._false_filter()
                 return {"$and": [{name: {"$exists": True}}, {name: {"$ne": None}}]}
             condition = {name: {"$in" if operator == "in" else "$nin": operands}}
-            if operator == "not_in" or None in operands:
-                guards: list[_Document] = [{name: {"$exists": True}}]
-                if operator == "not_in":
-                    guards.append({name: {"$ne": None}})
-                guards.append(condition)
-                return {"$and": guards}
+            if operator == "not_in":
+                return {"$and": [{name: {"$exists": True}}, {name: {"$ne": None}}, condition]}
             return condition
         if operator in {"contains", "contains_any", "contains_all"}:
             if field.type_ != "list":

python/packages/azure-documentdb/tests/azure_documentdb/test_vector_store.py

@@ -320,6 +320,23 @@ def test_empty_membership_semantics(collection):
     }
 
 
+def test_membership_never_matches_null_operands(collection):
+    assert collection._prepare_filter(Filter("category", "in", [None, "database"])) == {
+        "category": {"$in": ["database"]}
+    }
+    assert collection._prepare_filter(Filter("category", "in", [None])) == {"_id": {"$exists": False}}
+    assert collection._prepare_filter(Filter("category", "not_in", [None, "database"])) == {
+        "$and": [
+            {"category": {"$exists": True}},
+            {"category": {"$ne": None}},
+            {"category": {"$nin": ["database"]}},
+        ]
+    }
+    assert collection._prepare_filter(Filter("category", "not_in", [None])) == {
+        "$and": [{"category": {"$exists": True}}, {"category": {"$ne": None}}]
+    }
+
+
 def test_filter_type_mismatches_preserve_bool_number_distinction(collection):
     assert collection._prepare_filter(Filter("number", "eq", True)) == {"_id": {"$exists": False}}
     assert collection._prepare_filter(Filter("flag", "eq", 1)) == {"_id": {"$exists": False}}