public V get(final int keyPartA, final int keyPartB) {
        final long key = compoundKey(keyPartA, keyPartB);

        return map.get(key);
    }
@Test
    public void shouldReturnNullWhenNotFoundItem() {
        final int keyPartA = 3;
        final int keyPartB = 7;

        assertNull(map.get(keyPartA, keyPartB));
    }