BUG: Fix style.background_gradient() for nullable dtype (ex: Int64) series with pd.NA values (#50713)

* Fix style.background_gradient() for Int64 series with null values

* Update whatsnew

* Use the correct issue number

* Response to comments: move entry in whatsnew, include github issue in test, and check results against expected values from a regular float series

* Update doc/source/whatsnew/v2.0.0.rst

Co-authored-by: Patrick Hoefler <61934744+phofl@users.noreply.github.com>

Co-authored-by: Patrick Hoefler <61934744+phofl@users.noreply.github.com>

Author: dhendry

doc/source/whatsnew/v2.0.0.rst

@@ -1080,7 +1080,7 @@ ExtensionArray
 
 Styler
 ^^^^^^
--
+- Fix :meth:`~pandas.io.formats.style.Styler.background_gradient` for nullable dtype :class:`Series` with ``NA`` values (:issue:`50712`)
 -
 
 Metadata

pandas/io/formats/style.py

@@ -3619,7 +3619,7 @@ def _background_gradient(
     Color background in a range according to the data or a gradient map
     """
     if gmap is None:  # the data is used the gmap
-        gmap = data.to_numpy(dtype=float)
+        gmap = data.to_numpy(dtype=float, na_value=np.nan)
     else:  # else validate gmap against the underlying data
         gmap = _validate_apply_axis_arg(gmap, "gmap", float, data)
 

pandas/tests/io/formats/style/test_matplotlib.py

@@ -260,6 +260,16 @@ def test_background_gradient_gmap_wrong_series(styler_blank):
         styler_blank.background_gradient(gmap=gmap, axis=None)._compute()
 
 
+def test_background_gradient_nullable_dtypes():
+    # GH 50712
+    df1 = DataFrame([[1], [0], [np.nan]], dtype=float)
+    df2 = DataFrame([[1], [0], [None]], dtype="Int64")
+
+    ctx1 = df1.style.background_gradient()._compute().ctx
+    ctx2 = df2.style.background_gradient()._compute().ctx
+    assert ctx1 == ctx2
+
+
 @pytest.mark.parametrize(
     "cmap",
     ["PuBu", mpl.colormaps["PuBu"]],