Theme(background_color=nothing) not respected

[Roger Herikstad]

When using Gadfly through Jupyter, I can create a plot with transparent background like this

pp = plot(x=rand(10), y=rand(10), Geom.point, Theme(panel_fill=colorant"white", background_color=nothing))
draw(PDF("/tmp/test.pdf", 10cm, 10cm), pp)

However, when I do this from the REPL using Immerse, the resulting PDF has a white background.