Traceback (most recent call last):
  File ".../matplotlib/backends/backend_qt5.py", line 475, in _draw_idle
    self.draw()
  File ".../matplotlib/backends/backend_agg.py", line 406, in draw
    self.figure.draw(self.renderer)
  File ".../matplotlib/artist.py", line 74, in draw_wrapper
    result = draw(artist, renderer, *args, **kwargs)
  File ".../matplotlib/artist.py", line 51, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File ".../matplotlib/figure.py", line 2734, in draw
    mimage._draw_list_compositing_images(
  File ".../matplotlib/image.py", line 132, in _draw_list_compositing_images
    a.draw(renderer)
  File ".../matplotlib/artist.py", line 51, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File ".../matplotlib/_api/deprecation.py", line 431, in wrapper
    return func(*inner_args, **inner_kwargs)
  File ".../matplotlib/axes/_base.py", line 2925, in draw
    mimage._draw_list_compositing_images(renderer, self, artists)
  File ".../matplotlib/image.py", line 132, in _draw_list_compositing_images
    a.draw(renderer)
  File ".../matplotlib/artist.py", line 51, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File ".../matplotlib/legend.py", line 614, in draw
    self._legend_box.draw(renderer)
  File ".../matplotlib/offsetbox.py", line 368, in draw
    c.draw(renderer)
  File ".../matplotlib/offsetbox.py", line 368, in draw
    c.draw(renderer)
  File ".../matplotlib/offsetbox.py", line 368, in draw
    c.draw(renderer)
  [Previous line repeated 1 more time]
  File ".../matplotlib/offsetbox.py", line 694, in draw
    c.draw(renderer)
  File ".../matplotlib/artist.py", line 51, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File ".../matplotlib/collections.py", line 1009, in draw
    super().draw(renderer)
  File ".../matplotlib/artist.py", line 51, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File ".../matplotlib/collections.py", line 380, in draw
    len(facecolors) == 1 and len(edgecolors) == 1 and
TypeError: object of type 'NoneType' has no len()