cdm/src/main/java/ucar/nc2/units/DateType.java
public boolean before(DateType d) {
    if (d.isPresent()) return true;
    if (isPresent()) return false;
    return date.isBefore(d.getCalendarDate());
  }
public boolean before(DateType d) {
    if (d.isPresent()) return true;
    if (isPresent()) return false;
    return date.isBefore(d.getCalendarDate());
  }
Is this date before the given date. if d.isPresent, always true, else if this.isPresent, false.

@param d test against this date
@return true if this date before the given date