#vulnerable code 
                                @Override
    public Set<K> keySet(String cacheTitle) {
        Iterator it = cacheManager.getCache(cacheTitle).iterator();
        Set<K> set = new HashSet<>();
        while (it.hasNext()) {
            Cache.Entry<K, T> entry = (Cache.Entry<K, T>) it.next();
            set.add((K) entry.getKey());
        }
        return set;
    } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public Set<K> keySet(String cacheTitle) {
        Cache cache = this.cacheManager.getCache(cacheTitle);
        if (null == cache) {
            return new HashSet<>();
        }
        Iterator it = cache.iterator();
        Set<K> set = new HashSet<>();
        while (it.hasNext()) {
            Cache.Entry<K, T> entry = (Cache.Entry<K, T>) it.next();
            set.add((K) entry.getKey());
        }
        return set;
    }