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
element= getParent(element);
						if (element != null) {
							newSelection= new StructuredSelection(element);
							fViewer.setSelection(newSelection, true);
						}
					}
				} finally {
					fViewer.addSelectionChangedListener(fSelectionListener);
				}
			}
			return true;
		}
		return false;
	}
	
	private boolean isOnClassPath(IFile file) {
		IJavaProject jproject= JavaCore.create(file.getProject());
		return jproject.isOnClasspath(file);
	}
	/**
	 * Returns the element's parent.
	 * 
	 * @return the parent or <code>null</code> if there's no parent
	 */
	private Object getParent(Object element) {
		if (element instanceof IJavaElement)
			return ((IJavaElement)element).getParent();
		else if (element instanceof IResource)
			return ((IResource)element).getParent();