Difference between . and ./. for missing genotype in VCF

What is the difference between . and ./. for a missing genotype in a VCF file?
For example in one VCF record I have these two sample genotypes.

GT:AD:DP:GQ:MMQ:PGT:PID:PL    .:0,0:.:.:.:.:.:.       ./.:0,0:0:.:.:.:.:0,0,0

There is also is a difference in which genotype attributes are 0 or .