code: public void setMinDate(@Nullable Calendar minDate) {
          this.minDate = minDate;
          // update the date picker (even if it is not used right now)
          if(minDate == null)
              datePickerDialog.setMinDate(MINIMUM_POSSIBLE_DATE);
          else if(maxDate != null && compareCalendarDates(minDate, maxDate) > 0)
              throw new IllegalArgumentException("Minimum date must be before maximum date!");
          else
              datePickerDialog.setMinDate(new CalendarDay(minDate));
          updateEnabledItems();
      }
docs: Sets the minimum allowed date.
  Spinner items and dates in the date picker before the given date will get disabled.
  @param minDate The minimum date, or null to clear the previous min date.