Bug 75711 AstProvider should not create AST if requested by SelectionListenerWithASTManager
3.1 M2 If SelectionListenerWithASTManager waits for an AST and the editor closes we should not create an AST for that one but return null instead.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
/**
			 * {@inheritDoc}
			 */
			public void propertyChange(PropertyChangeEvent event) {
				if (getFilter().isFiltered(event))
					return;
				
				if (event.getNewValue() == null)
					fOptions.remove(event.getProperty());
				else
					fOptions.put(event.getProperty(), event.getNewValue());
				
				firePropertyChangeEvent(event.getProperty(), event.getOldValue(), event.getNewValue());
			}
		}
		
		private ListenerList fListeners= new ListenerList();
		
		private IPropertyChangeListener fListener= new PropertyChangeListener();
		
		private Map fOptions;
		
		private IPreferenceStore fMockupPreferenceStore;