#vulnerable code 
                             public <T> Key<T> save(String kind, T entity) {
		entity = ProxyHelper.unwrap(entity);
		DBCollection dbColl = getDB().getCollection(kind);
		return save(dbColl, entity, defConcern);
	} 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public <T> Key<T> save(String kind, T entity) {
		entity = ProxyHelper.unwrap(entity);
		DBCollection dbColl = getDB().getCollection(kind);
		return save(dbColl, entity, getWriteConcern(entity));
	}