Support normalize_kwargs(None) (== {}).

There's quite a few places where it's natural to pass None to
normalize_kwargs, so directly support that in normalize_kwargs instead
of having to do it at each call site.

Author: anntzer

lib/matplotlib/axes/_axes.py

@@ -3868,23 +3868,20 @@ def line_props_with_rcdefaults(subkey, explicit, zdelta=0,
             d['zorder'] = zorder + zdelta
             if not use_marker:
                 d['marker'] = ''
-            if explicit is not None:
-                d.update(cbook.normalize_kwargs(explicit, mlines.Line2D))
+            d.update(cbook.normalize_kwargs(explicit, mlines.Line2D))
             return d
 
         # box properties
         if patch_artist:
-            final_boxprops = dict(
-                linestyle=rcParams['boxplot.boxprops.linestyle'],
-                linewidth=rcParams['boxplot.boxprops.linewidth'],
-                edgecolor=rcParams['boxplot.boxprops.color'],
-                facecolor=('white' if rcParams['_internal.classic_mode'] else
-                           rcParams['patch.facecolor']),
-                zorder=zorder,
-            )
-            if boxprops is not None:
-                final_boxprops.update(
-                    cbook.normalize_kwargs(boxprops, mpatches.PathPatch))
+            final_boxprops = {
+                'linestyle': rcParams['boxplot.boxprops.linestyle'],
+                'linewidth': rcParams['boxplot.boxprops.linewidth'],
+                'edgecolor': rcParams['boxplot.boxprops.color'],
+                'facecolor': ('white' if rcParams['_internal.classic_mode']
+                              else rcParams['patch.facecolor']),
+                'zorder': zorder,
+                **cbook.normalize_kwargs(boxprops, mpatches.PathPatch)
+            }
         else:
             final_boxprops = line_props_with_rcdefaults('boxprops', boxprops,
                                                         use_marker=False)

lib/matplotlib/cbook/__init__.py

@@ -1714,8 +1714,10 @@ def normalize_kwargs(kw, alias_mapping=None, required=(), forbidden=(),
 
     Parameters
     ----------
-    kw : dict
-        A dict of keyword arguments.
+    kw : dict or None
+        A dict of keyword arguments.  None is explicitly supported and treated
+        as an empty dict, to support functions with an optional parameter of
+        the form ``props=None``.
 
     alias_mapping : dict or Artist subclass or Artist instance, optional
         A mapping between a canonical name to a list of
@@ -1747,6 +1749,9 @@ def normalize_kwargs(kw, alias_mapping=None, required=(), forbidden=(),
     """
     from matplotlib.artist import Artist
 
+    if kw is None:
+        return {}
+
     # deal with default value of alias_mapping
     if alias_mapping is None:
         alias_mapping = dict()

lib/matplotlib/tests/test_cbook.py

@@ -309,6 +309,7 @@ def test_sanitize_sequence():
 )
 
 pass_mapping = (
+    (None, {}, {}),
     ({'a': 1, 'b': 2}, {'a': 1, 'b': 2}, {}),
     ({'b': 2}, {'a': 2}, {'alias_mapping': {'a': ['a', 'b']}}),
     ({'b': 2}, {'a': 2},

lib/matplotlib/widgets.py

@@ -1826,11 +1826,10 @@ class ToolHandles:
 
     def __init__(self, ax, x, y, marker='o', marker_props=None, useblit=True):
         self.ax = ax
-        props = dict(marker=marker, markersize=7, markerfacecolor='w',
-                     linestyle='none', alpha=0.5, visible=False,
-                     label='_nolegend_')
-        props.update(cbook.normalize_kwargs(marker_props, Line2D._alias_map)
-                     if marker_props is not None else {})
+        props = {'marker': marker, 'markersize': 7, 'markerfacecolor': 'w',
+                 'linestyle': 'none', 'alpha': 0.5, 'visible': False,
+                 'label': '_nolegend_',
+                 **cbook.normalize_kwargs(marker_props, Line2D._alias_map)}
         self._markers = Line2D(x, y, animated=useblit, **props)
         self.ax.add_line(self._markers)
         self.artist = self._markers
@@ -2000,8 +1999,7 @@ def onselect(eclick: MouseEvent, erelease: MouseEvent)
             props = dict(markeredgecolor='r')
         else:
             props = dict(markeredgecolor=rectprops.get('edgecolor', 'r'))
-        props.update(cbook.normalize_kwargs(marker_props, Line2D._alias_map)
-                     if marker_props is not None else {})
+        props.update(cbook.normalize_kwargs(marker_props, Line2D._alias_map))
         self._corner_order = ['NW', 'NE', 'SE', 'SW']
         xc, yc = self.corners
         self._corner_handles = ToolHandles(self.ax, xc, yc, marker_props=props,