minor ticks with showMinorTicks: false causes "Cannot call method 'css' of undefined" in .jqplot.LinearAxisRenderer.prototype.pack
i'm trying to build a chart which will have more grid lines than ticks. the obvious way to do that seems to be using minor ticks with showMinorTicks: false. i have a custom (hacked for now) axis render that calls setTick with isMinor = true, but that causes .jqplot.LinearAxisRenderer.prototype.pack to blow up when it tries to set css on a non-existent element.
trivial patch attached.