code: public void setTimezone(ICalProperty property, TimezoneAssignment timezone) {
  		if (timezone == null) {
  			TimezoneAssignment existing = propertyTimezones.remove(property);
  			if (existing != null && existing != defaultTimezone && !propertyTimezones.values().contains(existing)) {
  				assignments.remove(existing);
  			}
  			return;
  		}
  
  		assignments.add(timezone);
  		propertyTimezones.put(property, timezone);
  	}
docs: Assigns a timezone to a specific property.
  @param property the property
  @param timezone the timezone or null to format the property according to
  the default timezone (see {@link #setDefaultTimezone}).