RuntimeError: CGContextRef is NULL with draw_artist about matplotlib HOT 5 CLOSED

import numpy as np

import matplotlib
matplotlib.use('MacOSX')
from matplotlib import pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(1,1,1)
image = ax.imshow(np.random.random((128, 128)))
def test_callback(event):
    ax.draw_artist(image)
fig.canvas.mpl_connect('button_press_event', test_callback)
plt.show()

Traceback (most recent call last):
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/backend_bases.py", line 1785, in button_press_event
    self.callbacks.process(s, mouseevent)
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/cbook.py", line 527, in process
    proxy(*args, **kwargs)
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/cbook.py", line 405, in __call__
    return mtd(*args, **kwargs)
  File "test_draw_artist.py", line 11, in test_callback
    ax.draw_artist(image)
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/axes.py", line 2098, in draw_artist
    a.draw(self._cachedRenderer)
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/artist.py", line 54, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/image.py", line 352, in draw
    gc = renderer.new_gc()
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/backends/backend_macosx.py", line 97, in new_gc
    self.gc.save()
RuntimeError: CGContextRef is NULL