Bug 189636 Custom rule template failing
Null poonter exception being thrown when trying to add a custom rule which is causing the rule cretion to fail. Also there is a minor typo in the rule template string.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
*            The viewer that this content service will be associated with.
	 */
	public NavigatorContentService(String aViewerId, StructuredViewer aViewer) {
		this(aViewerId);
		structuredViewerManager = new StructuredViewerManager(aViewer);
	}
	public String[] getVisibleExtensionIds() {
		List visibleExtensionIds = new ArrayList();
		NavigatorContentDescriptor[] descriptors = CONTENT_DESCRIPTOR_REGISTRY
				.getAllContentDescriptors();
		for (int i = 0; i < descriptors.length; i++) {
			if (assistant.isVisible(descriptors[i].getId())) {
				visibleExtensionIds.add(descriptors[i].getId());
			}
		}
		if (visibleExtensionIds.isEmpty()) {
			return NO_EXTENSION_IDS;
		}
		return (String[]) visibleExtensionIds
				.toArray(new String[visibleExtensionIds.size()]);
	}
	public INavigatorContentDescriptor[] getVisibleExtensions() {
		List visibleDescriptors = new ArrayList();
		NavigatorContentDescriptor[] descriptors = CONTENT_DESCRIPTOR_REGISTRY
				.getAllContentDescriptors();
		for (int i = 0; i < descriptors.length; i++) {
			if (assistant.isVisible(descriptors[i].getId())) {
				visibleDescriptors.add(descriptors[i]);
			}
		}