Deprecated. Don't use for new development and try to migrate existing uses.
This function extracts the persons sex from a swedish personal identity number (personnummer).
Supported input formats:
yymmddNNNK
yymmdd-NNNK
yymmdd+NNNK
YYyymmddNNNK
The return value is "M" if male and "F" if female. Invalid or incorrectly formatted personal identity numbers give a return value of null.