@Override
    public void putAll(Map<? extends K, ? extends V> m) {
        checkNotNull(m, "The passed in map cannot be null.");
        m.forEach((k, v) -> items.put(serializer.encode(k), serializer.encode(v)));
    }
@Test
    public void testPutAll() throws Exception {
        //Tests adding of an outside map
        Map<Integer, Integer> testMap = Maps.newHashMap();
        fillMap(10);
        map.putAll(testMap);
        for (int i = 0; i < 10; i++) {
            assertTrue("The map should contain the current 'i' value.", map.containsKey(i));
            assertTrue("The map should contain the current 'i' value.", map.containsValue(i));
        }
    }