Fix heatmap norm=None issue (#3276)

* Fix heatmap  issue.

* Update seaborn/matrix.py

Co-authored-by: Michael Waskom <[email protected]>

* Fix condition

* Add test for explicit `norm=None`.

---------

Co-authored-by: Michael Waskom <[email protected]>

Author: stefanistrate

seaborn/matrix.py

@@ -298,7 +298,7 @@ def plot(self, ax, cax, kws):
 
         # setting vmin/vmax in addition to norm is deprecated
         # so avoid setting if norm is set
-        if "norm" not in kws:
+        if kws.get("norm") is None:
             kws.setdefault("vmin", self.vmin)
             kws.setdefault("vmax", self.vmax)
 

tests/test_matrix.py

@@ -265,6 +265,20 @@ def test_cmap_with_properties(self):
         hm = mat._HeatMapper(self.df_unif, **kws)
         npt.assert_array_equal(cmap(np.inf), hm.cmap(np.inf))
 
+    def test_explicit_none_norm(self):
+
+        vals = np.linspace(.2, 1, 9)
+        cmap = mpl.cm.binary
+        _, (ax1, ax2) = plt.subplots(2)
+
+        mat.heatmap([vals], vmin=0, cmap=cmap, ax=ax1)
+        fc_default_norm = ax1.collections[0].get_facecolors()
+
+        mat.heatmap([vals], vmin=0, norm=None, cmap=cmap, ax=ax2)
+        fc_explicit_norm = ax2.collections[0].get_facecolors()
+
+        npt.assert_array_almost_equal(fc_default_norm, fc_explicit_norm, 2)
+
     def test_ticklabels_off(self):
         kws = self.default_kws.copy()
         kws['xticklabels'] = False