Zero exists, just not for the Gregorian calendar that follows the Anno Domini calendar numbering system (BC/AD). It is very true for Julian calendars that follow the astronomical year numbering system (BCE/CE) as well as Gregorian calendars that follow the ISO8601:2004 standard (no unit), as well as Holocene calendar, and numerous Hindu/Buddhist calendars.
Zero exists, just not for the Gregorian calendar that follows the Anno Domini calendar numbering system (BC/AD). It is very true for Julian calendars that follow the astronomical year numbering system (BCE/CE) as well as Gregorian calendars that follow the ISO8601:2004 standard (no unit), as well as Holocene calendar, and numerous Hindu/Buddhist calendars.
1 BC = 0 BCE = 10000HE -> 1AD = 1CE = 10001HE