Bug 92777 [Contributions] Spec clarification: ContributionItem.getParent() can return null
bundles/org.eclipse.jface/src/org/eclipse/jface/action/ContributionItem.java
*/
    protected ContributionItem() {
        this(null);
    }
    /**
     * Creates a contribution item with the given (optional) id.
     * The given id is used to find items in a contribution manager,
     * and for positioning items relative to other items.
     *
     * @param id the contribution item identifier, or <code>null</code>
     */
    protected ContributionItem(String id) {
        this.id = id;
    }
    /**
     * The default implementation of this <code>IContributionItem</code>
     * method does nothing. Subclasses may override.
     */
    public void dispose() {
    }
    /**
     * The default implementation of this <code>IContributionItem</code>
     * method does nothing. Subclasses may override.
     */
    public void fill(Composite parent) {
    }
    /**
     * The default implementation of this <code>IContributionItem</code>
     * method does nothing. Subclasses may override.
     */