From 365448dc665f6d49f3d3071a6c3a04aaccacb3d2 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sat, 4 Nov 2023 18:50:32 -0400
Subject: [PATCH] BUG: Index.isin raising for arrow strings and null set
 (#55821)

---
 doc/source/whatsnew/v2.1.3.rst     |  2 +-
 pandas/core/arrays/string_arrow.py |  4 +++-
 pandas/tests/indexes/test_base.py  | 12 ++++++++++--
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/doc/source/whatsnew/v2.1.3.rst b/doc/source/whatsnew/v2.1.3.rst
index 3b1cd1c152baa..31ab01f171b4a 100644
--- a/doc/source/whatsnew/v2.1.3.rst
+++ b/doc/source/whatsnew/v2.1.3.rst
@@ -22,7 +22,7 @@ Fixed regressions
 Bug fixes
 ~~~~~~~~~
 - Bug in :meth:`DatetimeIndex.diff` raising ``TypeError`` (:issue:`55080`)
--
+- Bug in :meth:`Index.isin` raising for Arrow backed string and ``None`` value (:issue:`55821`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_213.other:
diff --git a/pandas/core/arrays/string_arrow.py b/pandas/core/arrays/string_arrow.py
index ae020ec2f599f..1c2ecd4684e2f 100644
--- a/pandas/core/arrays/string_arrow.py
+++ b/pandas/core/arrays/string_arrow.py
@@ -222,7 +222,9 @@ def isin(self, values) -> npt.NDArray[np.bool_]:
         if not len(value_set):
             return np.zeros(len(self), dtype=bool)
 
-        result = pc.is_in(self._pa_array, value_set=pa.array(value_set))
+        result = pc.is_in(
+            self._pa_array, value_set=pa.array(value_set, type=self._pa_array.type)
+        )
         # pyarrow 2.0.0 returned nulls, so we explicily specify dtype to convert nulls
         # to False
         return np.array(result, dtype=np.bool_)
diff --git a/pandas/tests/indexes/test_base.py b/pandas/tests/indexes/test_base.py
index 0c32149124ac6..828700573c7ea 100644
--- a/pandas/tests/indexes/test_base.py
+++ b/pandas/tests/indexes/test_base.py
@@ -9,7 +9,7 @@
 
 from pandas.compat import IS64
 from pandas.errors import InvalidIndexError
-from pandas.util._test_decorators import async_mark
+import pandas.util._test_decorators as td
 
 from pandas.core.dtypes.common import (
     is_any_real_numeric_dtype,
@@ -921,6 +921,14 @@ def test_isin_empty(self, empty):
         result = index.isin(empty)
         tm.assert_numpy_array_equal(expected, result)
 
+    @td.skip_if_no("pyarrow")
+    def test_isin_arrow_string_null(self):
+        # GH#55821
+        index = Index(["a", "b"], dtype="string[pyarrow_numpy]")
+        result = index.isin([None])
+        expected = np.array([False, False])
+        tm.assert_numpy_array_equal(result, expected)
+
     @pytest.mark.parametrize(
         "values",
         [
@@ -1235,7 +1243,7 @@ def test_cached_properties_not_settable(self):
         with pytest.raises(AttributeError, match="Can't set attribute"):
             index.is_unique = False
 
-    @async_mark()
+    @td.async_mark()
     async def test_tab_complete_warning(self, ip):
         # https://github.com/pandas-dev/pandas/issues/16409
         pytest.importorskip("IPython", minversion="6.0.0")