@Override
    public Processor<KIn, VIn, KOut, VOut> get() {
        return new KStreamMapProcessor();
    }
@Test
    public void testKeyValueMapperResultNotNull() {
        final KStreamMap<String, Integer, String, Integer> supplier = new KStreamMap<>((key, value) -> null);
        final Throwable throwable = assertThrows(NullPointerException.class,
                () -> supplier.get().process(new Record<>("K", 0, 0L)));
        assertThat(throwable.getMessage(), is("The provided KeyValueMapper returned null which is not allowed."));
    }