FILTER column in vcf file from HaplotypeCaller

I used a cohort in running HaplotypeCaller. Some of values in the FILTER column of the resulting vcf file are ".", what does that mean?

Here is one example (not all columns included):

#CHROM  POS     ID      REF     ALT     QUAL    FILTER
22      16084134        .       A       C       152.03  .