Write application indicator with no icon

I wrote an application indicator that displays information about my monthly network consumption. I do not want it to have an icon next to the text I display. How do I write an application indicator without an icon?

The code I use to initialize my indicator is:

self.indicator = appindicator.Indicator.new("VooMeter", "network", appindicator.IndicatorCategory.SYSTEM_SERVICES)

Reading the documentation I can not find the value to put instead of "network"

After some code tries, I couldn't find a way either and reading the docs, I don't think it's possible. Here's something interesting from the label property:

The label will not be shown unless there is an icon as well.

So, if there is a way to disable the icon, it won't even show the label.

I had the same problem. As a workaround I have used one pixel wide transparent image as icon.