@Test
    public void shouldRoundTripNull() {
        assertThat(serde.serializeParts(null, null), nullValue());
        assertThat(mergeChangeArraysIntoSingleLegacyFormattedArray(null), nullValue());
        assertThat(FullChangeSerde.decomposeLegacyFormattedArrayIntoChangeArrays(null), nullValue());
        assertThat(serde.deserializeParts(null, null), nullValue());
    }
We used to serialize a Change into a single byte[]. Now, we don't anymore, but we still keep this logic here
so that we can produce the legacy format to test that we can still deserialize it.
streams/src/test/java/org/apache/kafka/streams/kstream/internals/FullChangeSerdeTest.java