code: public final synchronized void addVetoableChangeListener(
              VetoableChangeListener listener) {
          if (listener == null) {
              return;
          }
          if (vetoSupport == null) {
              vetoSupport = new VetoableChangeSupport(this);
          }
          vetoSupport.addVetoableChangeListener(listener);
      }
docs: Adds a VetoableChangeListener to the listener list. The listener is registered for all bound
  properties of this class.<p>
  
  If listener is {@code null}, no exception is thrown and no action is performed.
  
  @param listener the VetoableChangeListener to be added
  
  @see #removeVetoableChangeListener(String, VetoableChangeListener)
  @see #addVetoableChangeListener(String, VetoableChangeListener)
  @see #getVetoableChangeListeners()