public V get(final int keyPartA, final int keyPartB)
    {
        return unmapNullValue(getMapping(keyPartA, keyPartB));
    }
@Test
    void shouldReturnNullWhenNotFoundItem()
    {
        final int keyPartA = 3;
        final int keyPartB = 7;

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