code: public static void setDefault(DateTimeZone zone) throws SecurityException {
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
              sm.checkPermission(new JodaTimePermission("DateTimeZone.setDefault"));
          }
          if (zone == null) {
              throw new IllegalArgumentException("The datetime zone must not be null");
          }
          cDefault.set(zone);
      }
docs: Sets the default time zone.
  <p>
  NOTE: Calling this method does <i>not</i> set the {@code java.util.TimeZone} default.
  
  @param zone  the default datetime zone object, must not be null
  @throws IllegalArgumentException if the zone is null
  @throws SecurityException if the application has insufficient security rights