jpgraph with line graph

[tsukushi]

i'm trying to plot 2 line graphs in ONE graph
y1axis data takes x-axis range from 1-31 (for example, days in a month)
y2axis data takes x-axis range from 10-20 (for example, just a range of days in a month)

when i try to plot it on the same graph, i get the error of:
Cant draw unspecified Y-Scale:
You're either
1)Specified an Y axis for autoscaling but forgot to supply any plots
2)Specified a scale manually but forgot to specify the tick steps.

I guess this is because i have no
y2axis data from 1-9 & 21-31

any sample code on how i can draw 2 line graphs which does not have EVERY value on the x-axis?

Thanks