Bug 219909 [DataBinding] UnmodifiableObservableValue
UnmodifiableObservableValue with test cases
bundles/org.eclipse.core.databinding/src/org/eclipse/core/databinding/observable/Observables.java
* @return an empty observable set.
	 */
	public static IObservableSet emptyObservableSet() {
		return emptyObservableSet(Realm.getDefault(), null);
	}
	/**
	 * Returns an empty observable set of the given element type. The returned
	 * set continues to work after it has been disposed of and can be disposed
	 * of multiple times.
	 * 
	 * @param elementType
	 *            the element type of the returned set
	 * @return an empty observable set
	 * @since 1.1
	 */
	public static IObservableSet emptyObservableSet(Object elementType) {
		return emptyObservableSet(Realm.getDefault(), elementType);
	}
	/**
	 * Returns an empty observable set belonging to the given realm. The
	 * returned set continues to work after it has been disposed of and can be
	 * disposed of multiple times.
	 * 
	 * @param realm
	 *            the realm of the returned set
	 * @return an empty observable set.
	 */
	public static IObservableSet emptyObservableSet(Realm realm) {
		return emptyObservableSet(realm, null);
	}