Bug 219909 [DataBinding] UnmodifiableObservableValue
UnmodifiableObservableValue with test cases
bundles/org.eclipse.core.databinding/src/org/eclipse/core/databinding/observable/Observables.java
public static IObservableSet unmodifiableObservableSet(IObservableSet set) {
		if (set == null) {
			throw new IllegalArgumentException("Set parameter cannot be null"); 
		}
		return new UnmodifiableObservableSet(set);
	}
	/**
	 * Returns an empty observable list. The returned list continues to work
	 * after it has been disposed of and can be disposed of multiple times.
	 * 
	 * @return an empty observable list.
	 */
	public static IObservableList emptyObservableList() {
		return emptyObservableList(Realm.getDefault(), null);
	}
	/**
	 * Returns an empty observable list of the given element type. The returned
	 * list continues to work after it has been disposed of and can be disposed
	 * of multiple times.
	 * 
	 * @param elementType
	 *            the element type of the returned list
	 * @return an empty observable list
	 * @since 1.1
	 */
	public static IObservableList emptyObservableList(Object elementType) {
		return emptyObservableList(Realm.getDefault(), elementType);
	}
	/**
	 * Returns an empty observable list belonging to the given realm. The