fix(vector_stores): return None from Redis.get() for missing IDs (#5625)

Co-authored-by: ly-wang19 <ly-wang19@users.noreply.github.com>
Co-authored-by: Kartik <kartik.labhshetwar@mem0.ai>

tests/vector_stores/test_redis.py

@@ -113,3 +113,18 @@ def test_list_with_filter_builds_query():
 
     query = mock_index.search.call_args[0][0]
     assert query.query_string() == "@user_id:{alice}"
+
+
+def test_get_returns_none_for_missing_id():
+    """get() must return None for a missing id.
+
+    redisvl's SearchIndex.fetch() returns None when the id is not found, so the
+    old code raised ``TypeError: 'NoneType' object is not subscriptable`` on
+    ``result["hash"]``. Every other vector store returns None for a missing id,
+    and Memory relies on it (``if existing_memory is None``), so get() must too.
+    """
+    db, mock_index = _make_redis_db()
+    mock_index.fetch.return_value = None
+
+    assert db.get("missing_id") is None
+    mock_index.fetch.assert_called_once_with("missing_id")