Bug 79916 [Viewers] isDisposed check needed in AbstractTreeViewer#internalRemove
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* This method is typically used when preserving the interesting state of a
     * viewer; <code>setExpandedElements</code> is used during the restore.
     * </p>
     * 
     * @return the array of expanded elements
     * @see #setExpandedElements
     */
    public Object[] getExpandedElements() {
        ArrayList v = new ArrayList();
        internalCollectExpanded(v, getControl());
        return v.toArray();
    }
    /**
     * Returns whether the node corresponding to the given element is expanded
     * or collapsed.
     * 
     * @param element
     *           the element
     * @return <code>true</code> if the node is expanded, and <code>false</code>
     *         if collapsed
     */
    public boolean getExpandedState(Object element) {
        Assert.isNotNull(element);
        Widget item = findItem(element);
        if (item instanceof Item)
            return getExpanded((Item) item);
        return false;
    }
    /**
     * Returns the number of child items of the given SWT control.