Multiple comparisons of groups with emmeans of a clm: Error in UseMethod("vcoc"): no applicable methos for 'vcov' applied to an object of class "clm"

Question

I'm trying to make a post-hoc tests with emmean/lsmeans for multiple comparisons of groups. In fact, I'm trying to recreate an example found here: https://rcompanion.org/handbook/G_11.html.

Thus, I have a model which looks like this:

library(ordinal)

model = clm(Likert.f ~ Instructor + Question + Instructor:Question,
            data = Data,
            threshold="symmetric")


library(car)

library(RVAideMemoire)

Anova(model,
      type = "II")

Then I'm trying to explore the group separation for the interaction effect:

library(lsmeans)

marginal = lsmeans(model,
                      pairwise ~ Instructor + Question,
                      adjust="tukey")        ### Tukey-adjusted comparisons

marginal

cld(marginal,
    alpha   = 0.05,
    Letters = letters,      ### Use lower-case letters for .group
    adjust  = "tukey")       ### Tukey-adjusted comparisons  

But I get the following error:

Error in UseMethod("vcoc"): no applicable methos for 'vcov' applied to an object of class "clm"

I also tried the same with emmeans, but with the same error.

Can someone guide me what is wrong? :)