Bug 81426 Package Explorer shows nothing after drill into working set, then show projects
I200412160800 - switch Package Explorer to working sets - context menu > Go Into a working set - Show > Projects -> view is empty -> view toolbar button 'Up to Working Sets' does not do anything
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
Tree tree= getTree();
			TreeItem[] selection= tree.getSelection();
			List result= new ArrayList(selection.length);
			List treePaths= new ArrayList();
			for (int i= 0; i < selection.length; i++) {
				TreeItem item= selection[i];
				Object element= getElement(item);
				if (element == null)
					continue;
				if (!result.contains(element)) {
					result.add(element);
				}
				treePaths.add(createTreePath(item));
			}
			return new MultiElementSelection(this, result, (TreePath[])treePaths.toArray(new TreePath[treePaths.size()]));
		}
		private TreePath createTreePath(TreeItem item) {
			List result= new ArrayList();
			result.add(item.getData());
			TreeItem parent= item.getParentItem();
			while (parent != null) {
				result.add(parent.getData());
				parent= parent.getParentItem();
			}
			Collections.reverse(result);
			return new TreePath(result.toArray());
		}
		private Object getElement(TreeItem item) {
			Object result= item.getData();
			if (result == null)