fill_between() doesn't accept all possible linestyles (esp. empty ones..)

import matplotlib.pyplot as plt
plt.fill_between([1,2,3], [4,5,6], 5, linestyle="None")

ValueError: Do not know how to convert None to dashes

The same for "" and " "

[ mpl: 1.5.1; python 2.7.9; OpenSUSE; user install by pip (pip install --user matplotlib) ]