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
*         have a <b>triggerPoints</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */
	public Set findDescriptorsByTriggerPoint(Object anElement) {
		NavigatorContentDescriptor descriptor = getSourceOfContribution(anElement);
		Set result = new TreeSet(ExtensionPriorityComparator.INSTANCE);
		if (descriptor != null) {
			result.add(descriptor);
		}
		result.addAll(CONTENT_DESCRIPTOR_REGISTRY
				.findDescriptorsForTriggerPoint(anElement, assistant));
		return result;
	}
	/**
	 * Search for extensions that declare the given element in their
	 * <b>possibleChildren</b> expression.
	 * 
	 * @param anElement
	 *            The element to use in the query
	 * @return The set of {@link INavigatorContentDescriptor}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>possibleChildren</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */
	public Set findDescriptorsWithPossibleChild(Object anElement) {
		return findDescriptorsWithPossibleChild(anElement, true);
	}
	
	/**
	 * Search for extensions that declare the given element in their