I want to know the difference between zero and '.' for an Exac value/GnomAD MAF value in an annotated VCF ? What is the difference between MAF is 0 as not found in the population and MAF is '.' as doesn't exist? Like for example, when the variant ExAC All MAF value is '.' what does this mean? I have lots of variants with this MAF in ExAC and GnomAD value both in VEP and Annovar annotated VCFs.