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
* (Non-Javadoc)
	 *  
	 * @see INavigatorContentService#getContentDescriptorById(String)
	 */
	public INavigatorContentDescriptor getContentDescriptorById(String anExtensionId) {
		return CONTENT_DESCRIPTOR_REGISTRY.getContentDescriptor(anExtensionId); 
	}
	
	/** 
	 * 
	 * @param anExtensionId The id used to define the <b>org.eclipse.ui.navigator.navigatorContent/navigatorContent</b> extension.
	 * @return An instance of the content extension for the given extension id. May return <b>null</b> if the id is invalid.
	 */
	public INavigatorContentExtension getContentExtensionById(String anExtensionId) {
		NavigatorContentDescriptor descriptor = CONTENT_DESCRIPTOR_REGISTRY.getContentDescriptor(anExtensionId);
		if(descriptor != null)
			return getExtension(descriptor);
		return null;
	}
	/**
	 * Search for extensions that declare the given element in their
	 * <b>triggerPoints</b> expression.
	 * 
	 * @param anElement
	 *            The element to use in the query
	 * @return The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>triggerPoints</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */