[Data] Raise ValueError when the data sort key is None (ray-project#4…

…8969)

Closes: ray-project#48926
ray-project#48927
<!-- Please give a short summary of the change and the problem this
solves. -->

Signed-off-by: Superskyyy <yihaochen@apache.org>
Signed-off-by: Richard Liaw <rliaw@berkeley.edu>
Signed-off-by: Hao Chen <chenh1024@gmail.com>
Co-authored-by: Richard Liaw <rliaw@berkeley.edu>
Co-authored-by: Hao Chen <chenh1024@gmail.com>
Signed-off-by: Connor Sanders <connor@elastiflow.com>

python/ray/data/dataset.py

@@ -2435,11 +2435,12 @@ def std(
     @PublicAPI(api_group=SSR_API_GROUP)
     def sort(
         self,
-        key: Union[str, List[str], None] = None,
+        key: Union[str, List[str]],
         descending: Union[bool, List[bool]] = False,
         boundaries: List[Union[int, float]] = None,
     ) -> "Dataset":
         """Sort the dataset by the specified key column or key function.
+        The `key` parameter must be specified (i.e., it cannot be `None`).
 
         .. note::
             The `descending` parameter must be a boolean, or a list of booleans.
@@ -2488,7 +2489,12 @@ def sort(
 
         Returns:
             A new, sorted :class:`Dataset`.
+
+        Raises:
+            ``ValueError``: if the sort key is None.
         """
+        if key is None:
+            raise ValueError("The 'key' parameter cannot be None for sorting.")
         sort_key = SortKey(key, descending, boundaries)
         plan = self._plan.copy()
         op = Sort(

python/ray/data/tests/test_optimize.py

@@ -294,7 +294,7 @@ def test_optimize_lazy_reuse_base_data(
 
 
 def test_require_preserve_order(ray_start_regular_shared):
-    ds = ray.data.range(100).map_batches(lambda x: x).sort()
+    ds = ray.data.range(100).map_batches(lambda x: x).sort("id")
     assert ds._plan.require_preserve_order()
     ds2 = ray.data.range(100).map_batches(lambda x: x).zip(ds)
     assert ds2._plan.require_preserve_order()