fix(duckdb): handle null-typed scalars in to_pyarrow()

ibis/backends/duckdb/converter.py

@@ -18,6 +18,12 @@ def convert_Array(s, dtype, pandas_type):
 
 
 class DuckDBPyArrowData(PyArrowData):
+    @classmethod
+    def convert_scalar(cls, scalar: pa.Scalar, dtype: dt.DataType) -> pa.Scalar:
+        if dtype.is_null():
+            return pa.scalar(None)
+        return super().convert_scalar(scalar, dtype)
+
     @classmethod
     def convert_column(cls, column: pa.Array, dtype: dt.DataType) -> pa.Array:
         if dtype.is_null():

ibis/backends/duckdb/tests/test_client.py

@@ -445,7 +445,16 @@ def test_pyarrow_batches_chunk_size(con):  # 10443
         next(batches)
 
 
-def test_create_table_with_nulls(con):
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        dict(obj=ibis.memtable({"a": [None]})),
+        dict(obj=ibis.memtable({"a": [None]}), schema=ibis.schema({"a": "null"})),
+        dict(schema=ibis.schema({"a": "null"})),
+    ],
+    ids=["obj", "obj-schema", "schema"],
+)
+def test_create_table_with_nulls(con, kwargs):
     t = ibis.memtable({"a": [None]})
     schema = t.schema()
 
@@ -454,13 +463,5 @@ def test_create_table_with_nulls(con):
 
     name = gen_name("duckdb_all_nulls")
 
-    match = "NULL typed columns"
-
-    with pytest.raises(com.IbisTypeError, match=match):
-        con.create_table(name, obj=t)
-
-    with pytest.raises(com.IbisTypeError, match=match):
-        con.create_table(name, obj=t, schema=schema)
-
-    with pytest.raises(com.IbisTypeError, match=match):
-        con.create_table(name, schema=schema)
+    with pytest.raises(com.IbisTypeError, match="NULL typed columns"):
+        con.create_table(name, **kwargs)

ibis/backends/tests/test_export.py

@@ -624,8 +624,7 @@ def test_scalar_to_memory(limit, awards_players, output_format, converter):
     assert converter(res) is None
 
 
-# flink
-@pytest.mark.notyet(
+mark_notyet_nulls = pytest.mark.notyet(
     [
         "clickhouse",
         "exasol",
@@ -639,9 +638,25 @@ def test_scalar_to_memory(limit, awards_players, output_format, converter):
         "trino",
     ],
     raises=com.IbisTypeError,
-    reason="unable to handle null typed columns as input",
+    reason="unable to handle null types as input",
 )
-def test_all_null_column(con):
+
+
+@mark_notyet_nulls
+def test_all_null_table(con):
     t = ibis.memtable({"a": [None]})
     result = con.to_pyarrow(t)
     assert pat.is_null(result["a"].type)
+
+
+@mark_notyet_nulls
+def test_all_null_column(con):
+    t = ibis.memtable({"a": [None]})
+    result = con.to_pyarrow(t.a)
+    assert pat.is_null(result.type)
+
+
+def test_all_null_scalar(con):
+    e = ibis.literal(None)
+    result = con.to_pyarrow(e)
+    assert pat.is_null(result.type)