spgrass6 and null values

Hello list,

while exporting vector maps form GRASS to R using readVECT6(spgrass6), 
null values in attributes become zeroes in R, and makes them 
undistinguishable from real zero-valued attributes.

I'm making a work-around, by previously replacing zeroes by 0.5 in GRASS 
(wich is an impossible value) and then reverting once in R.

But i wonder if there is a correct way of doing this that i didn't find. 
If not, i suggest to add the feature of passing null values to NAs and 
viceversa.

Greetings
       Facundo Mu?oz
       Universidad de Valencia
       Spain