If the samples HipStr is joint calling all match the reference, is a variant record/line outputted. In many cases, it is important not only to see the variant sites, but also evidence for non-variant sites (think gVCFs).
Yes. If HipSTR genotypes an STR and no variants are detected across any of the samples, it'll automatically output a VCF record with no alternate alleles in which all samples have a 0/0 genotype.
If the samples HipStr is joint calling all match the reference, is a variant record/line outputted. In many cases, it is important not only to see the variant sites, but also evidence for non-variant sites (think gVCFs).