Fix pandas-dev#56844: function mask handling None values as condition

This commit addresses an issue where using pandas.NA in conjunction with the mask() method resulted in unexpected behavior. The problem arose when comparing a Series containing pandas.NA with a condition within mask(), causing inconsistencies in the output. This fix ensures that pandas.NA behaves consistently with False in logical operations within mask().

Author: mafaldam

doc/source/whatsnew/v3.0.0.rst

@@ -329,6 +329,7 @@ Performance improvements
 Bug fixes
 ~~~~~~~~~
 - Fixed bug in :class:`SparseDtype` for equal comparison with na fill value. (:issue:`54770`)
+- Fixed bug in :func:`mask` to handle NaN values in condition of function. (:issue:`56844`)
 - Fixed bug in :meth:`.DataFrameGroupBy.median` where nat values gave an incorrect result. (:issue:`57926`)
 - Fixed bug in :meth:`DataFrame.cumsum` which was raising ``IndexError`` if dtype is ``timedelta64[ns]`` (:issue:`57956`)
 - Fixed bug in :meth:`DataFrame.join` inconsistently setting result index name (:issue:`55815`)

pandas/core/generic.py

@@ -9960,6 +9960,9 @@ def mask(
         cond = common.apply_if_callable(cond, self)
         other = common.apply_if_callable(other, self)
 
+        if isinstance(cond, ABCDataFrame | ABCSeries):
+            cond = cond.fillna(False)
+
         # see gh-21891
         if not hasattr(cond, "__invert__"):
             cond = np.array(cond)

pandas/tests/frame/indexing/test_mask.py

@@ -150,3 +150,11 @@ def test_mask_inplace_no_other():
     df.mask(cond, inplace=True)
     expected = DataFrame({"a": [np.nan, 2], "b": ["x", np.nan]})
     tm.assert_frame_equal(df, expected)
+
+
+def test_mask_with_NA():
+    df = DataFrame({"A": [0, 1, 2]})
+    cond = Series([-1, 1, None]).convert_dtypes() < 0
+    result = df.mask(cond, other=100)
+    expected = DataFrame({"A": [100, 1, 2]})
+    tm.assert_frame_equal(result, expected)