Enable sorting on column with nulls using query-planning (#15639)

Related to #15027

Authors:
  - Richard (Rick) Zamora (https://github.com/rjzamora)

Approvers:
  - Lawrence Mitchell (https://github.com/wence-)
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

URL: #15639

python/dask_cudf/dask_cudf/backends.py

@@ -307,7 +307,7 @@ def categorical_dtype_cudf(categories=None, ordered=False):
 @tolist_dispatch.register((cudf.Series, cudf.BaseIndex))
 @_dask_cudf_nvtx_annotate
 def tolist_cudf(obj):
-    return obj.to_arrow().to_pylist()
+    return obj.to_pandas().tolist()
 
 
 @is_categorical_dtype_dispatch.register(

python/dask_cudf/dask_cudf/tests/test_sort.py

@@ -72,7 +72,7 @@ def test_sort_repartition():
     dd.assert_eq(len(new_ddf), len(ddf))
 
 
-@xfail_dask_expr("dask-expr code path fails with nulls")
+@xfail_dask_expr("missing null support", lt_version="2024.5.1")
 @pytest.mark.parametrize("na_position", ["first", "last"])
 @pytest.mark.parametrize("ascending", [True, False])
 @pytest.mark.parametrize("by", ["a", "b", ["a", "b"]])