handleDefaults = function(contIn, contOut, attr, dflt) {
        var attrs = {};
        attrs[attr] = attributes;
        return Lib.coerce(contIn, contOut, attrs, attr, dflt);
      }
Check that a candidate date is from the same calendar and is valid.
            @memberof UmmAlQuraCalendar
            @private
            @param year {CDate|number} The date to validate or the year to validate.
            @param month {number} The month to validate.
            @param day {number} The day to validate.
            @param error {string} Error message if invalid.
            @throws Error if different calendars used or invalid date.