code: protected void firePropertyChange(PropertyChangeEvent event) {
      if (isEventDispatchEnabled()) {
        Assert.notNull(event, "The PropertyChangeEvent cannot be null!");
        if (propertyChangeSupport.hasListeners(event.getPropertyName())) {
          propertyChangeSupport.firePropertyChange(event);
        }
      }
    }
docs: Notifies all PropertyChangeListeners of a property change event occurring on this Bean.
  
  @param event the PropertyChangeEvent indicating the property who's value is changing.
  @throws NullPointerException if the PropertyChangeEvent is null.
  @see java.beans.PropertyChangeEvent
  @see java.beans.PropertyChangeListener
  @see java.beans.PropertyChangeSupport#firePropertyChange(java.beans.PropertyChangeEvent)
  @see java.beans.PropertyChangeSupport#hasListeners(String)