> using Gadfly
> plot(x=rand(10), y=rand(10), Theme(grid_color=nothing))
MethodError: `hex` has no method matching hex(::Void)
in render at /home/juser/.julia/v0.4/Gadfly/src/guide.jl:611
in render_prepared at /home/juser/.julia/v0.4/Gadfly/src/Gadfly.jl:794
in render at /home/juser/.julia/v0.4/Gadfly/src/Gadfly.jl:721
in writemime at /home/juser/.julia/v0.4/Gadfly/src/Gadfly.jl:854
in sprint at iostream.jl:211
in display_dict at /home/juser/.julia/v0.4/IJulia/src/execute_request.jl:29