Does encode throw away commas and just use them for parity? if so then..

[knormoyle]

I was trying to understand the encode function for a character and couldn't understand comma handling

Does a comma just get thrown away after xoring it into parity generation?

if so, how does a sentence like this get parsed correctly, if you have some empty fields in the middle, and good fields after that?

$GNGSA,A,3,30,14,09,04,,,,,,,,,1.37,0.77,1.14,10B
$GNGSA,A,3,68,78,67,69,,,,,,,,,1.37,0.77,1.14,20C
$GNGSA,A,3,05,09,06,25,03,,,,,,,,1.37,0.77,1.14,30C
$GNGSA,A,3,12,23,11,08,,,,,,,,,1.37,0.77,1.14,40F

seems like you need to retain commas to correctly identify fields in a finished sentence?
I thought fields aren't extracted until you get a finished sentence.