Bug 22994 Choose Package subdialog of New Class dialog crashes if source dir is not on java build path [dialogs]
There is no code for checking whether given IPackageFragmentRoot exists. Simmilar problem is in Choose Source Dir dialog - it allows you to select project even if it is not a source folder.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/wizards/NewContainerWizardPage.java
protected static final String CONTAINER= "NewContainerWizardPage.container"; 
	
	protected IStatus fContainerStatus;
	private StringButtonDialogField fContainerDialogField;
		
	/*
	 * package fragment root corresponding to the input type (can be null)
	 */
	private IPackageFragmentRoot fCurrRoot;
	
	private IWorkspaceRoot fWorkspaceRoot;