Regression in mpl2.0b3 compared to 1.5.1:

bar([0, 1], [2, 3], color="none", edgecolor="k", linewidth=None)

doesn't draw edges for the bars. The docstring (which btw has a weird linebreak) states:

    linewidth : scalar or array-like, optional
        width of bar edge(s). If None, use default
        linewidth; If 0, don't draw edges.
        default: None

Perhaps due to a change in the defaults, I'm not sure? But even if this was the case at least the docstring should be updated to indicate which rcparam gives the default, and state that this default is zero.