perl -MDevel::Peek -e'Dump($ARGV[0])'
SV = NULL(0x0) at 0x55a8c4978560
  REFCNT = 2147483639
  FLAGS = (READONLY,PROTECT)

perl -MDevel::Peek -e'Dump(undef)'
SV = NULL(0x0) at 0x55923aa70560
  REFCNT = 2147483639
  FLAGS = (READONLY,PROTECT)