To help us understand and resolve your issue please check that you have provided
the information below.

• [ v2.x ] Matplotlib version, Python version and Platform (Windows, OSX, Linux ...)
• [ source ] How did you install Matplotlib and Python (pip, anaconda, from source ...)
• If possible please supply a Short, Self Contained, Correct, Example
  that demonstrates the issue i.e a small piece of code which reproduces the issue
  and can be run with out any other (or as few as possible) external dependencies.

plt.imshow(np.ones((5, 5)) * np.nan)

• If this is an image generation bug attach a screenshot demonstrating the issue.
  

Also got some user warnings

 /home/tcaswell/.virtualenvs/dd_35/lib/python3.5/site-packages/numpy/ma/core.py:4089: UserWarning: Warning: converting a masked element to nan.
  warnings.warn("Warning: converting a masked element to nan.")
/home/tcaswell/source/p/matplotlib/lib/matplotlib/colors.py:581: RuntimeWarning: invalid value encountered in less
  cbook._putmask(xa, xa < 0.0, -1)
/home/tcaswell/source/p/matplotlib/lib/matplotlib/cm.py:275: RuntimeWarning: invalid value encountered in less
  rgba[:, :, 3][x < 0.0] = 0

• [ always ] If this is a regression (Used to work in an earlier version of Matplotlib), please
  note where it used to work.