I’m trying to manually convert a set of configuration properties to an object using Spring.

My target class looks like this:

class ComplexConfigurationProperties {
  private final Map<String, ComplexObject> objects;

  public ComplexConfigurationProperties(Map<String, ComplexObject> objects) {
    this.objects = objects;
  }
}

And my Converter looks like this:

class CustomConverter implements Converter<Map<String, Object>, ComplexObject> {

  @Override
  public ComplexObject convert(Map<String, Object> source) {
    ComplexObject result;
    // do some stuff
    return result;
  }
}

My test for this looks like this:

@Test
void test() {
  DefaultConversionService conversionService = new DefaultConversionService();
  conversionService.addConverter(new CustomConverter());
  ComplexConfigurationProperties props = new Binder(
      Collections.singleton(
          new MapConfigurationPropertySource(
              Map.of(
                  "prefix.objects.a.property1", "property1",
                  "prefix.objects.a.property2", "property2"
              )
          )
      ), null,
      conversionService
  ).bind("prefix", ComplexConfigurationProperties.class).get();

  assertNotNull(props);
}

The binding result is always null and my custom converter is never used. Now my question is: what did I do wrong? Do I need to use a different source type in the converter? Is what I’m trying to do not possible?
I couldn’t find anything regarding the conversion of complex types in the documentation.