#vulnerable code 
                             public void checkElementStyleGroup(Element element) {
		StyleGroup oldGroup = getGroup(getElementGroup(element));

		// Get the old element "dynamic" status.

		boolean isDyn = oldGroup.isElementDynamic(element);

		// Get the old event set for the given element.

		StyleGroup.ElementEvents events = null;

		if (oldGroup != null)
			events = oldGroup.getEventsFor(element);

		// Remove the element from its old style and add it to insert it in the
		// correct style.

		removeElement(element);
		addElement_(element);

		// Eventually push the events on the new style group.

		StyleGroup newGroup = getGroup(getElementGroup(element));

		if (newGroup != null && events != null) {
			for (String event : events.events)
				pushEventFor(element, event);
		}

		for (StyleGroupListener listener : listeners)
			listener.elementStyleChanged(element, oldGroup, newGroup);

		// Eventually set the element as dynamic, if it was.

		if (newGroup != null && isDyn)
			newGroup.pushElementAsDynamic(element);
	} 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public void checkElementStyleGroup(Element element) {
		StyleGroup oldGroup = getGroup(getElementGroup(element));

		// Get the old element "dynamic" status.

		boolean isDyn = false;

		// Get the old event set for the given element.

		StyleGroup.ElementEvents events = null;

		if (oldGroup != null) {
			isDyn = oldGroup.isElementDynamic(element);
			events = oldGroup.getEventsFor(element);
		}

		// Remove the element from its old style and add it to insert it in the
		// correct style.

		removeElement(element);
		addElement_(element);

		// Eventually push the events on the new style group.

		StyleGroup newGroup = getGroup(getElementGroup(element));

		if (newGroup != null && events != null) {
			for (String event : events.events)
				pushEventFor(element, event);
		}

		for (StyleGroupListener listener : listeners)
			listener.elementStyleChanged(element, oldGroup, newGroup);

		// Eventually set the element as dynamic, if it was.

		if (newGroup != null && isDyn)
			newGroup.pushElementAsDynamic(element);
	}