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. 


Thanks
`0` is zero. 

`.` is for null: data is not available/ unknown /missing 


