diff --git a/python/packages/azure-cosmos/agent_framework_azure_cosmos/_vector_store.py b/python/packages/azure-cosmos/agent_framework_azure_cosmos/_vector_store.py
index 13141c589df..15e8a044fd4 100644
--- a/python/packages/azure-cosmos/agent_framework_azure_cosmos/_vector_store.py
+++ b/python/packages/azure-cosmos/agent_framework_azure_cosmos/_vector_store.py
@@ -1004,7 +1004,7 @@ def _translate_filter(
                 return "false" if operator == "eq" else f"IS_DEFINED({access})"
             parameter = _add_parameter(parameters, value)
             if operator == "eq":
-                return f"(IS_DEFINED({access}) AND {access} = {parameter})"
+                return f"(IS_DEFINED({access}) AND NOT IS_NULL({access}) AND {access} = {parameter})"
             return f"(IS_DEFINED({access}) AND (IS_NULL({access}) OR {access} != {parameter}))"
         if operator in ("gt", "gte", "lt", "lte", "between"):
             if field.type_ not in ("str", "int", "float"):
diff --git a/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store.py b/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store.py
index 108b12f3788..8819799ba9d 100644
--- a/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store.py
+++ b/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store.py
@@ -691,9 +691,14 @@ async def test_full_batch_item_size_and_json_preflight() -> None:
         ),
         (
             Filter("text", "eq", "O'Reilly"),
-            '(IS_DEFINED(c["content"]) AND c["content"] = @filter_0)',
+            '(IS_DEFINED(c["content"]) AND NOT IS_NULL(c["content"]) AND c["content"] = @filter_0)',
             ["O'Reilly"],
         ),
+        (
+            FilterGroup("not", [Filter("optional", "eq", "value")]),
+            '(NOT (IS_DEFINED(c["optional"]) AND NOT IS_NULL(c["optional"]) AND c["optional"] = @filter_0))',
+            ["value"],
+        ),
         (
             Filter("text", "ne", "x"),
             '(IS_DEFINED(c["content"]) AND (IS_NULL(c["content"]) OR c["content"] != @filter_0))',
@@ -765,7 +770,7 @@ async def test_full_batch_item_size_and_json_preflight() -> None:
     ],
 )
 def test_filter_translation_matches_portable_semantics(
-    expression: Filter,
+    expression: Filter | FilterGroup,
     clause: str,
     values: list[Any],
 ) -> None:
@@ -790,7 +795,7 @@ def test_filter_groups_and_rejections() -> None:
     clause, parameters = collection._prepare_filter(group)
     assert clause == (
         '((IS_DEFINED(c["count"]) AND NOT IS_NULL(c["count"]) AND c["count"] >= @filter_0) '
-        'AND (NOT (IS_DEFINED(c["active"]) AND c["active"] = @filter_1)))'
+        'AND (NOT (IS_DEFINED(c["active"]) AND NOT IS_NULL(c["active"]) AND c["active"] = @filter_1)))'
     )
     assert [item["value"] for item in parameters] == [1, False]
     for expression, exception in (
@@ -958,7 +963,7 @@ async def test_filtered_get_query_is_parameterized_and_bounded() -> None:
     kwargs = container.query_items.call_args.kwargs
     query = kwargs["query"]
     assert "hello" not in query
-    assert 'WHERE (IS_DEFINED(c["content"]) AND c["content"] = @filter_0)' in query
+    assert 'WHERE (IS_DEFINED(c["content"]) AND NOT IS_NULL(c["content"]) AND c["content"] = @filter_0)' in query
     assert 'ORDER BY c["count"] DESC OFFSET @skip LIMIT @top' in query
     assert kwargs["parameters"] == [
         {"name": "@filter_0", "value": "hello"},
diff --git a/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store_integration.py b/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store_integration.py
index b51ffe849d8..bd1b5e510a1 100644
--- a/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store_integration.py
+++ b/python/packages/azure-cosmos/tests/azure_cosmos/test_vector_store_integration.py
@@ -269,6 +269,8 @@ async def test_disposable_vector_database_crud_filter_and_search() -> None:
         }
         assert await default_collection.get(filter=Filter("count", "eq", True)) == []
         assert await default_collection.get(filter=Filter("active", "eq", 1)) == []
+        not_value = FilterGroup("not", [Filter("optional", "eq", "value")])
+        assert {item["key"] for item in await default_collection.get(filter=not_value)} == {"one", "three"}
 
         missing_optional = {**multi_records[0], "id": "missing"}
         missing_optional.pop("optional")