Code example for PropertyChangeSupport

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            throw new IllegalArgumentException("Null 'key' argument.");
        } 
        this.key = key;
        this.description = description;
//        this.listeners = new EventListenerList(); 
        this.propertyChangeSupport = new PropertyChangeSupport(this);
        this.notify = true;
    } 
 
    /** 
     * Returns the key for the series. 
     * 
     * @return The series key (never <code>null</code>). 
     * 
     * @see #setKey(Comparable) 
     */ 
    public Comparable getKey() {
        return this.key;
    } 
 
    /**