@Nullable
    private <T> T extractFieldMeta(JavaType classType, JavaType fieldType, String fieldName,
                                   Function<AnnotatedElement, @Nullable T> extractor) {
        if (request) {
            return extractRequestFieldMeta(classType, fieldType, fieldName, extractor);
        } else {
            return extractResponseFieldMeta(classType, fieldType, fieldName, extractor);
        }
    }
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