Bug 210115 [DataBinding] NPE when getter called on disposed observable
bundles/org.eclipse.core.databinding/src/org/eclipse/core/databinding/observable/ObservableTracker.java
* receiver has been read from". This lets callers know that they can rely
	 * on automatic updates from the object without explicitly attaching a
	 * listener.
	 * 
	 * @param observable
	 */
	public static void getterCalled(IObservable observable) {
		Assert.isTrue(observable.getRealm().isCurrent());
		Set lastObservableSet = (Set) currentObservableSet.get();
		if (lastObservableSet == null) {
			return;
		}
		IChangeListener lastChangeListener = (IChangeListener) currentChangeListener
				.get();
		IStaleListener lastStaleListener = (IStaleListener) currentStaleListener
				.get();
		boolean added = false;
		if (lastObservableSet != null) {
			added = lastObservableSet.add(new IdentityWrapper(observable));
		}
		
		if (added && lastChangeListener != null) {
			observable.addChangeListener(lastChangeListener);
		}
		if (added && lastStaleListener != null) {
			observable.addStaleListener(lastStaleListener);
		}
	}
}