Loess -- Gadfly -- SVG/PDF "False" Error

Specific Domains Visualization
1

Dear Julia Experts— on macOS, julia 0.6.2, Feb 2018:

using Loess
xs = 10 .* rand(100);
ys = sin(xs) .+ 0.5 * rand(100);
model = loess(xs, ys);
us = collect(minimum(xs):0.1:maximum(xs))
vs = predict(model, us)

using Gadfly
p = plot(x=xs, y=ys, Geom.point, Guide.xlabel("x"), Guide.ylabel("y"),
         layer(Geom.line, x=us, y=vs))
draw(SVG("loess.svg", 6inch, 3inch), p)

spawns and draws a nice figure in the web browser, but the SVG draw just returns “false” without error detail.

I then installed Cairo and Fontconfig, and rm ~/.julia/lib/v0.6/Compose.ji, and restarted the REPL, then the equivalent pdf() creation worked

draw(PDF("loess.pdf", 6inch, 3inch), p)

My suggestion is this: [a] could the SVG draw error be more explanatory; [b] could the loess docs be updated for it?