From 0f4634dc3432826be3f9cdb5e0badf93ed29212c Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Thu, 17 Mar 2022 13:31:00 +0000
Subject: [PATCH 1/2] REGR: DataFrame.replace when the replacement value was
 explitly None

---
 doc/source/whatsnew/v1.4.2.rst             |  1 +
 pandas/core/internals/blocks.py            |  7 +++++++
 pandas/tests/frame/methods/test_replace.py | 14 ++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/doc/source/whatsnew/v1.4.2.rst b/doc/source/whatsnew/v1.4.2.rst
index 3523f691cae8f..7d63f36b11d43 100644
--- a/doc/source/whatsnew/v1.4.2.rst
+++ b/doc/source/whatsnew/v1.4.2.rst
@@ -19,6 +19,7 @@ Fixed regressions
 - Fixed memory performance regression in :meth:`Series.fillna` when called on a :class:`DataFrame` column with ``inplace=True`` (:issue:`46149`)
 - Provided an alternative solution for passing custom Excel formats in :meth:`.Styler.to_excel`, which was a regression based on stricter CSS validation. Examples available in the documentation for :meth:`.Styler.format` (:issue:`46152`)
 - Fixed regression in :meth:`DataFrame.replace` when a replacement value was also a target for replacement (:issue:`46306`)
+- Fixed regression in :meth:`DataFrame.replace` when the replacement value was explitly ``None`` when passed in a dictionary to ``to_replace`` (:issue:`45601`, :issue:`45836`)
 - Fixed regression when setting values with :meth:`DataFrame.loc` losing :class:`MultiIndex` names if :class:`DataFrame`  was empty before (:issue:`46317`)
 -
 
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 69f66973d0954..168b41652b735 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -778,6 +778,13 @@ def _replace_coerce(
                 mask=mask,
             )
         else:
+            if value is None:
+                # gh-45601, gh-45836
+                nb = self.astype(np.dtype(object), copy=False)
+                if nb is self and not inplace:
+                    nb = nb.copy()
+                putmask_inplace(nb.values, mask, value)
+                return [nb]
             return self.replace(
                 to_replace=to_replace, value=value, inplace=inplace, mask=mask
             )
diff --git a/pandas/tests/frame/methods/test_replace.py b/pandas/tests/frame/methods/test_replace.py
index 2eb300a8905b8..da13f2c16064e 100644
--- a/pandas/tests/frame/methods/test_replace.py
+++ b/pandas/tests/frame/methods/test_replace.py
@@ -676,6 +676,20 @@ def test_replace_numpy_nan(self, nulls_fixture):
         result = df.replace(to_replace, value).astype(dtype=dtype)
         tm.assert_frame_equal(result, expected)
 
+    def test_replace_NA_with_None(self):
+        # gh-45601
+        df = DataFrame({"value": [42, None]}).astype({"value": "Int64"})
+        result = df.replace({pd.NA: None})
+        expected = DataFrame({"value": [42, None]}, dtype=object)
+        tm.assert_frame_equal(result, expected)
+
+    def test_replace_NAT_with_None(self):
+        # gh-45836
+        df = DataFrame([pd.NaT, pd.NaT])
+        result = df.replace({pd.NaT: None, np.NaN: None})
+        expected = DataFrame([None, None])
+        tm.assert_frame_equal(result, expected)
+
     def test_replace_value_is_none(self, datetime_frame):
         orig_value = datetime_frame.iloc[0, 0]
         orig2 = datetime_frame.iloc[1, 0]

From 426741b359a9ac86181b8964b9a061a35aa35260 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Thu, 17 Mar 2022 13:43:53 +0000
Subject: [PATCH 2/2] typo

---
 doc/source/whatsnew/v1.4.2.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.4.2.rst b/doc/source/whatsnew/v1.4.2.rst
index 7d63f36b11d43..4cbb8118055af 100644
--- a/doc/source/whatsnew/v1.4.2.rst
+++ b/doc/source/whatsnew/v1.4.2.rst
@@ -19,7 +19,7 @@ Fixed regressions
 - Fixed memory performance regression in :meth:`Series.fillna` when called on a :class:`DataFrame` column with ``inplace=True`` (:issue:`46149`)
 - Provided an alternative solution for passing custom Excel formats in :meth:`.Styler.to_excel`, which was a regression based on stricter CSS validation. Examples available in the documentation for :meth:`.Styler.format` (:issue:`46152`)
 - Fixed regression in :meth:`DataFrame.replace` when a replacement value was also a target for replacement (:issue:`46306`)
-- Fixed regression in :meth:`DataFrame.replace` when the replacement value was explitly ``None`` when passed in a dictionary to ``to_replace`` (:issue:`45601`, :issue:`45836`)
+- Fixed regression in :meth:`DataFrame.replace` when the replacement value was explicitly ``None`` when passed in a dictionary to ``to_replace`` (:issue:`45601`, :issue:`45836`)
 - Fixed regression when setting values with :meth:`DataFrame.loc` losing :class:`MultiIndex` names if :class:`DataFrame`  was empty before (:issue:`46317`)
 -