Handle argument "facecolors=None" correctly in plot_surface() (matplotlib#24727)

* Handle keyword argument "facecolors=None" correctly in plot_surface

Author: ocastany

lib/mpl_toolkits/mplot3d/axes3d.py

@@ -1598,14 +1598,13 @@ def plot_surface(self, X, Y, Z, *, norm=None, vmin=None,
             rstride = int(max(np.ceil(rows / rcount), 1))
             cstride = int(max(np.ceil(cols / ccount), 1))
 
-        if 'facecolors' in kwargs:
-            fcolors = kwargs.pop('facecolors')
-        else:
+        fcolors = kwargs.pop('facecolors', None)
+
+        if fcolors is None:
             color = kwargs.pop('color', None)
             if color is None:
                 color = self._get_lines.get_next_color()
             color = np.array(mcolors.to_rgba(color))
-            fcolors = None
 
         cmap = kwargs.get('cmap', None)
         shade = kwargs.pop('shade', cmap is None)

lib/mpl_toolkits/mplot3d/tests/test_axes3d.py

@@ -608,6 +608,16 @@ def test_surface3d_masked():
     ax.view_init(30, -80, 0)
 
 
+@check_figures_equal(extensions=["png"])
+def test_plot_surface_None_arg(fig_test, fig_ref):
+    x, y = np.meshgrid(np.arange(5), np.arange(5))
+    z = x + y
+    ax_test = fig_test.add_subplot(projection='3d')
+    ax_test.plot_surface(x, y, z, facecolors=None)
+    ax_ref = fig_ref.add_subplot(projection='3d')
+    ax_ref.plot_surface(x, y, z)
+
+
 @mpl3d_image_comparison(['surface3d_masked_strides.png'])
 def test_surface3d_masked_strides():
     fig = plt.figure()