fix: always create TreeAhConfig in create_tree_ah_index()

Fixes #6222

Author: taimo3810

google/cloud/aiplatform/matching_engine/matching_engine_index.py

@@ -596,15 +596,10 @@ def create_tree_ah_index(
 
         """
 
-        algorithm_config = None
-        if (
-            leaf_node_embedding_count is not None
-            or leaf_nodes_to_search_percent is not None
-        ):
-            algorithm_config = matching_engine_index_config.TreeAhConfig(
-                leaf_node_embedding_count=leaf_node_embedding_count,
-                leaf_nodes_to_search_percent=leaf_nodes_to_search_percent,
-            )
+        algorithm_config = matching_engine_index_config.TreeAhConfig(
+            leaf_node_embedding_count=leaf_node_embedding_count,
+            leaf_nodes_to_search_percent=leaf_nodes_to_search_percent,
+        )
 
         config = matching_engine_index_config.MatchingEngineIndexConfig(
             dimensions=dimensions,

tests/unit/aiplatform/test_matching_engine_index.py

@@ -637,7 +637,12 @@ def test_create_tree_ah_index_empty_algorithm_config(self, create_index_mock):
             display_name=_TEST_INDEX_DISPLAY_NAME,
             metadata={
                 "config": {
-                    "algorithmConfig": None,
+                    "algorithmConfig": {
+                        "treeAhConfig": {
+                            "leafNodeEmbeddingCount": None,
+                            "leafNodesToSearchPercent": None,
+                        }
+                    },
                     "dimensions": _TEST_INDEX_CONFIG_DIMENSIONS,
                     "approximateNeighborsCount": _TEST_INDEX_APPROXIMATE_NEIGHBORS_COUNT,
                     "distanceMeasureType": _TEST_INDEX_DISTANCE_MEASURE_TYPE,