vcf file empty

Hi

I am getting an empty vcf file when I run below command
vg call -t 10 -r ./1000g.snarls ./1000g.xg -k ./alignment/sorted_A019_1000g.pack > ./alignment/sorted_A019_1000g_no_aug.vcf

All my input files contain data. Any suggestions on what could be the reason?

Thanks
Philge