Object resolve(ResolverContext ctx) {
        final Object resolved = resolver.apply(this, ctx);
        return shouldWrapValueAsOptional ? Optional.ofNullable(resolved)
                                         : resolved;
    }
Returns an attribute resolver which retrieves a value specified by {@code attrKeys}
from the {@link RequestContext}.
core/src/main/java/com/linecorp/armeria/internal/server/annotation/AnnotatedValueResolver.java