[GRASS-user] v.to.rast for a vectorial without Values

Greetings

I have created a Vectorial using GRASS vector digitizer without categories. This means that, When I do v.what over the polygons I get:

East: 630786.588235
North: 219567.632353
Map: A02
Mapset: landsat
Type: Area
Sq Meters: 2023087.825
Hectares: 202.309
Acres: 499.916
Sq Miles: 0.7811

But when i try to convert to rater I get an empty raster. Maybe I’m not “parameterizing the module in the right way”. How can I do that?
When I run v.to.rast I get:

Loading data…
Area centroid without category
Area centroid without category
Reading areas…
Reading features…
Writing raster map…
Converted areas: 2 of 2
Converted points/lines: 0 of 0
v.to.rast complete.

If this is not possible, How can I add a category to the vectorials in order to agfter that, run v.to.rast?

Thanks
Luisa