Question about carb calculatin

Hi all,

I have a little question about carb calculation, what if the dry matter came in negative number? I read somw where that this means the food has very little carb but does not know exatly how little it is!!

Is that right or no, because i am trying to find new feed and sone of them is not in the chart so i use a live calculater or i do the calculation and some of them come in negative like -4 or -27

If anyone can help i will be happy