When reaching the last class, the user obtains class NA

In the last step of a classification we need to add a pseudo class. The reference data for the pseudo class is build with the following code:

    if (last == T) {
      reference <- rbind(reference, rep(3000, ncol(reference)))
    }

With an hard coded value it is not possible to change it which can lead to the selection of the pseudo class leading to a NA as selected class.