calculateAgeAtDeath static method
Calculates the age at death based on the date of birth (DOB) and date of death (DOD).
Args: dob (DateTime?): The date of birth. dod (DateTime?): The date of death.
Returns:
int?: The calculated age at death, or null if either dob or dod
  is null, or if dod is before dob.
Implementation
static int? calculateAgeAtDeath({required DateTime? dob, required DateTime? dod}) {
  // Check if either dob or dod is null
  if (dob == null || dod == null) {
    return null;
  }
  // Check if dod is before dob
  if (dod.isBefore(dob)) {
    return null;
  }
  int age = dod.year - dob.year;
  // Adjust age if the birthday hasn't occurred yet in the dod year
  if (dod.month < dob.month || (dod.month == dob.month && dod.day < dob.day)) {
    age--;
  }
  return age;
}