static boolean isNullable(AnnotatedElement element) {
        return isAnnotatedNullable(element) || KotlinUtil.isMarkedNullable(element);
    }
A default {@link DescriptiveTypeInfoProvider} to create a {@link StructInfo} from a {@code typeDescriptor}.
If {@code typeDescriptor} is unknown type, Jackson is used to try to extract fields
and their metadata.
core/src/main/java/com/linecorp/armeria/internal/server/annotation/DefaultDescriptiveTypeInfoProvider.java