From 298d29e77ee1e4ee2c50e5e1ea25b2e0fd6c0408 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Mon, 31 Oct 2022 18:13:27 +0100
Subject: [PATCH] Backport PR #48234: REGR: Fix regression RecursionError when
 replacing numeric scalar with None

---
 doc/source/whatsnew/v1.5.2.rst              |  2 +-
 pandas/core/internals/blocks.py             |  6 ++++--
 pandas/tests/frame/methods/test_replace.py  | 12 ++++++++++++
 pandas/tests/series/methods/test_replace.py |  8 ++++++++
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/doc/source/whatsnew/v1.5.2.rst b/doc/source/whatsnew/v1.5.2.rst
index aaf00804262bb..4f6274b9084da 100644
--- a/doc/source/whatsnew/v1.5.2.rst
+++ b/doc/source/whatsnew/v1.5.2.rst
@@ -13,7 +13,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
--
+- Fixed regression in :meth:`Series.replace` raising ``RecursionError`` with numeric dtype and when specifying ``value=None`` (:issue:`45725`)
 -
 
 .. ---------------------------------------------------------------------------
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 9c6b3e506b1d4..5e95f83ddfd08 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -569,7 +569,6 @@ def replace(
         # Note: the checks we do in NDFrame.replace ensure we never get
         #  here with listlike to_replace or value, as those cases
         #  go through replace_list
-
         values = self.values
 
         if isinstance(values, Categorical):
@@ -608,7 +607,10 @@ def replace(
             return blocks
 
         elif self.ndim == 1 or self.shape[0] == 1:
-            blk = self.coerce_to_target_dtype(value)
+            if value is None:
+                blk = self.astype(np.dtype(object))
+            else:
+                blk = self.coerce_to_target_dtype(value)
             return blk.replace(
                 to_replace=to_replace,
                 value=value,
diff --git a/pandas/tests/frame/methods/test_replace.py b/pandas/tests/frame/methods/test_replace.py
index 177f3ec1b4504..f4de685688b00 100644
--- a/pandas/tests/frame/methods/test_replace.py
+++ b/pandas/tests/frame/methods/test_replace.py
@@ -1496,6 +1496,18 @@ def test_replace_list_with_mixed_type(
         result = obj.replace(box(to_replace), value)
         tm.assert_equal(result, expected)
 
+    @pytest.mark.parametrize("val", [2, np.nan, 2.0])
+    def test_replace_value_none_dtype_numeric(self, val):
+        # GH#48231
+        df = DataFrame({"a": [1, val]})
+        result = df.replace(val, None)
+        expected = DataFrame({"a": [1, None]}, dtype=object)
+        tm.assert_frame_equal(result, expected)
+
+        df = DataFrame({"a": [1, val]})
+        result = df.replace({val: None})
+        tm.assert_frame_equal(result, expected)
+
 
 class TestDataFrameReplaceRegex:
     @pytest.mark.parametrize(
diff --git a/pandas/tests/series/methods/test_replace.py b/pandas/tests/series/methods/test_replace.py
index 77c9cf4013bd7..126a89503d636 100644
--- a/pandas/tests/series/methods/test_replace.py
+++ b/pandas/tests/series/methods/test_replace.py
@@ -667,3 +667,11 @@ def test_replace_different_int_types(self, any_int_numpy_dtype):
         result = labs.replace(map_dict)
         expected = labs.replace({0: 0, 2: 1, 1: 2})
         tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize("val", [2, np.nan, 2.0])
+    def test_replace_value_none_dtype_numeric(self, val):
+        # GH#48231
+        ser = pd.Series([1, val])
+        result = ser.replace(val, None)
+        expected = pd.Series([1, None], dtype=object)
+        tm.assert_series_equal(result, expected)