SpringBoot Empty @DefaultValue cannot be used on collections, maps, arrays or optional values

I have this simple configuration:

@ConfigurationProperties("dummy")
public record TestRecord(@DefaultValue Set<String> values, @DefaultValue("default") String one) {
}

This fails with : Parameter of type java.util.Set<java.lang.String> must have a non-empty default value.

What I would like to get as a default value is an empty Set. Of course as a workaround, I can:

public Set<String> values() {
    return values == null ? Set.of() : values;
}

but considering there are any of these default collections/maps, I do not want to add an accessor for each of the properties. Is there are a way to make @DefaultValue "return" an empty Set? thank you.

Comment From: philwebb

@wind57 This looks like a duplicate of #18917 which should have been fixed in Spring Boot 2.2.7. Which version of Spring Boot are you using? Are you able to provide a sample application that shows the problem?

Comment From: wind57

@ConfigurationProperties("dummy")
public record TestRecord(@DefaultValue Set<String> values, @DefaultValue("default") String one) {

}

and a test:

    @Test
    void testSpringBindingFields() {
        new ApplicationContextRunner().withUserConfiguration(UnderTest.Config.class)
            .run(context -> {
                TestRecord props = context.getBean(TestRecord.class);
                assertThat(props).isNotNull();
                assertThat(props.one()).isEqualTo("default");
                assertThat(props.values().size()).isEqualTo(0);
            });
    }

    @Configuration
    @EnableConfigurationProperties(TestRecord.class)
    static class Config {

    }

This is for 3.0.0-M5. I am actually trying to simplify some code in spring-cloud-kubernetes , this were I spotted it.

thank you for looking into it.

Comment From: philwebb

Thanks, I misread our current code and thought that it dealt with collection types, but it doesn't. I think we should change that and allow @DefaultValue to mean an empty instance.

Comment From: wind57

That was fast! Thank you.

Comment From: wind57

would you happen to know when this one will reach spring-boot-3? just want to put a note for myself to slightly change some code when that happens, so that I do not forget; nothing more. thank you

Comment From: snicoll

@wind57 all fixes are merged forward at the same time as the fix itself. Please follow the linked issues for more details, that is https://github.com/spring-projects/spring-boot/issues/32564

Comment From: wind57

thank you.