Enable no op optimize (#19490)

src/lightning/data/processing/data_processor.py

@@ -724,7 +724,12 @@ class DataChunkRecipe(DataRecipe):
 
             size = sum([c["dim"] if c["dim"] is not None else c["chunk_size"] for c in config["chunks"]])
             num_bytes = sum([c["chunk_bytes"] for c in config["chunks"]])
-            data_format = tree_unflatten(config["config"]["data_format"], treespec_loads(config["config"]["data_spec"]))
+            if config["config"] is not None:
+                data_format = tree_unflatten(
+                    config["config"]["data_format"], treespec_loads(config["config"]["data_spec"])
+                )
+            else:
+                data_format = None
             num_chunks = len(config["chunks"])
 
             # The platform can't store more than 1024 entries.
@@ -735,7 +740,7 @@ class DataChunkRecipe(DataRecipe):
                 size=size,
                 num_bytes=num_bytes,
                 data_format=data_format,
-                compression=config["config"]["compression"],
+                compression=config["config"]["compression"] if config["config"] else None,
                 num_chunks=len(config["chunks"]),
                 num_bytes_per_chunk=num_bytes_per_chunk,
             )

src/lightning/data/processing/utilities.py

@@ -2,7 +2,7 @@ import io
 import os
 import urllib
 from contextlib import contextmanager
-from subprocess import Popen
+from subprocess import DEVNULL, Popen
 from typing import Any, Callable, List, Optional, Tuple, Union
 
 from lightning.data.constants import _IS_IN_STUDIO, _LIGHTNING_CLOUD_LATEST
@@ -134,7 +134,7 @@ def optimize_dns(enable: bool) -> None:
             f"sudo /home/zeus/miniconda3/envs/cloudspace/bin/python"
             f" -c 'from lightning.data.processing.utilities import _optimize_dns; _optimize_dns({enable})'"
         )
-        Popen(cmd, shell=True).wait()  # E501
+        Popen(cmd, shell=True, stdout=DEVNULL, stderr=DEVNULL).wait()  # E501
 
 
 def _optimize_dns(enable: bool) -> None:

tests/tests_data/processing/test_data_processor.py

@@ -1023,3 +1023,19 @@ def test_map_is_last(num_workers, expected, tmpdir):
     )
 
     assert sorted(os.listdir(tmpdir)) == expected
+
+
+def no_op(index):
+    pass
+
+
+def test_empty_optimize(tmpdir):
+    optimize(
+        no_op,
+        list(range(10)),
+        output_dir=str(tmpdir),
+        chunk_bytes="64MB",
+        num_workers=1,
+    )
+
+    assert os.listdir(tmpdir) == ["index.json"]