In Date::Calendar::Julian version 0.0.1, there was an arithmetic error when converting dates from Gregorian (or other) to a Julian 1st January. For example, when converting Gregorian 14 January 2020 to Julian, this would produce a "32 December 2019" and then the sanity checks defined in the class would trigger an exception.
So yesterday I have fixed this arithmetic error and I have released to CPAN6 version 0.0.2 of Date::Calendar::Julian. Thank you for your attention, Jean Forget