Handle string formatted None color values for line marker

Author: Seb Vetter

packages/python/plotly/plotly/matplotlylib/mplexporter/exporter.py

@@ -193,6 +193,10 @@ def draw_line(self, ax, line, force_trans=None):
         if (markerstyle['marker'] in ['None', 'none', None]
                 or markerstyle['markerpath'][0].size == 0):
             markerstyle = None
+        
+        if (markerstyle and markerstyle.get('facecolor') in ['None', 'none']):
+            markerstyle["facecolor"] = None
+            
         label = line.get_label()
         if markerstyle or linestyle:
             self.renderer.draw_marked_line(data=data, coordinates=coordinates,