public static String fromParts(String... parts) {
        return fromPartsAndSeparator(ID_SEPARATOR, parts);
    }
@Test
    void fromParts() {
        String id = IdUtils.fromParts("namespace", "flow");
        assertThat(id, notNullValue());
        assertThat(id, is("namespace_flow"));

        String idWithNull = IdUtils.fromParts(null, "namespace", "flow");
        assertThat(idWithNull, notNullValue());
        assertThat(idWithNull, is("namespace_flow"));
    }