protected void doubleNestedPropagateNull(Function<Query, ResultIterable<? extends TestBean>> mapFunction) {

        try (Query select = handle.select("select 'fourty-two' as nid")) {
            TestBean testBean = mapFunction.apply(select)
                .one();

            assertThat(testBean).isNotNull();
            assertThat(testBean.getNestedBean()).isNotNull();
            assertThat(testBean.getNestedBean().getId()).isEqualTo("fourty-two");

            testBean = mapFunction.apply(handle.select("select NULL as nid")).one();

            assertThat(testBean).isNull();
        }
    }
Test that propagateNull is bubbled up. If the property in the nested bean is null, not only null out the nested bean but the prent bean as well.
core/src/test/java/org/jdbi/v3/core/mapper/AbstractPropagateNullTest.java