diff --git a/checkpoint/orbax/checkpoint/base_pytree_checkpoint_handler.py b/checkpoint/orbax/checkpoint/base_pytree_checkpoint_handler.py
index a8dac3a3a..95592a6d7 100644
--- a/checkpoint/orbax/checkpoint/base_pytree_checkpoint_handler.py
+++ b/checkpoint/orbax/checkpoint/base_pytree_checkpoint_handler.py
@@ -25,6 +25,7 @@
 import json
 import time
 from typing import Any, List, Optional, Tuple, Union
+import uuid
 
 from absl import logging
 from etils import epath
@@ -40,6 +41,7 @@
 import tensorstore as ts
 
 
+
 PyTree = Any
 TupleKey = Tuple[str, ...]
 RestoreArgs = type_handlers.RestoreArgs
@@ -58,6 +60,7 @@
 METADATA_FILE = '_METADATA'
 
 
+
 def get_byte_limiter(concurrent_gb: int):
   async def _create_byte_limiter():
     # Wrap creation in async function to avoid issues on python<=3.9.
@@ -248,7 +251,8 @@ def __init__(
         to None, then all hosts will be considered as primary. It's useful in
         the case that all hosts are only working with local storage.
       type_handler_registry: a type_handlers.TypeHandlerRegistry. If not
-        specified, the global type handler registry will be used.
+        specified, the global type handler registry will be used. # BEGIN
+      enable_descriptor: If True, logs a Descriptor proto that contains lineage
     """
     self._concurrent_gb = concurrent_gb
     self._use_ocdbt = use_ocdbt
@@ -261,7 +265,7 @@ def __init__(
         '/jax/orbax/pytree_checkpoint_handler/init/ocdbt'
     )
 
-    self._thread_pool = futures.ThreadPoolExecutor(max_workers=1)
+    self._thread_pool = futures.ThreadPoolExecutor(max_workers=2)
 
   def get_param_names(self, item: PyTree) -> PyTree:
     """Gets parameter names for PyTree elements."""
@@ -418,10 +422,11 @@ async def async_save(
 
     if multihost.is_primary_host(self._primary_host):
       metadata_write_start_time = time.time()
-      metadata_future = self._write_metadata_file(
-          directory, param_infos, save_args, self._use_zarr3
+      commit_futures.append(
+          self._write_metadata_file(
+              directory, param_infos, save_args, self._use_zarr3
+          )
       )
-      commit_futures += [metadata_future]
       jax.monitoring.record_event_duration_secs(
           '/jax/checkpoint/write/async/metadata_write_duration_secs',
           time.time() - metadata_write_start_time,
@@ -723,7 +728,7 @@ def finalize(self, directory: epath.Path) -> None:
 
   def close(self):
     """Closes the handler. Called automatically by Checkpointer."""
-    pass
+    self._thread_pool.shutdown()
 
 
 @register_with_handler(BasePyTreeCheckpointHandler, for_save=True)
diff --git a/checkpoint/orbax/checkpoint/standard_checkpoint_handler_test_utils.py b/checkpoint/orbax/checkpoint/standard_checkpoint_handler_test_utils.py
index 1a3c32d5b..c783d6e53 100644
--- a/checkpoint/orbax/checkpoint/standard_checkpoint_handler_test_utils.py
+++ b/checkpoint/orbax/checkpoint/standard_checkpoint_handler_test_utils.py
@@ -230,11 +230,13 @@ def make_params():
       )
       test_utils.assert_tree_equal(self, params, restored)
 
-    def test_empty_pytrees(self):
+    def test_empty_error(self):
       """Test case."""
       with self.assertRaises(ValueError):
         self.handler.save(self.directory, args=self.save_args_cls({}))
 
+    def test_empty_dict_node(self):
+      """Test case."""
       item = {'a': {}, 'b': 3}
       self.handler.save(self.directory, args=self.save_args_cls(item))
       restored = self.handler.restore(
@@ -242,6 +244,8 @@ def test_empty_pytrees(self):
       )
       self.assertDictEqual(restored, item)
 
+    def test_empty_none_node(self):
+      """Test case."""
       item = {'c': None, 'd': 2}
       self.handler.save(self.directory, args=self.save_args_cls(item))
       restored = self.handler.restore(