Package check result: ERROR

Check: examples, Result: ERROR
  Running examples in ‘mlexperiments-Ex.R’ failed
  The error most likely occurred in:
  
  > base::assign(".ptime", proc.time(), pos = "CheckExEnv")
  > ### Name: MLCrossValidation
  > ### Title: R6 Class to perform cross-validation experiments
  > ### Aliases: MLCrossValidation
  > 
  > ### ** Examples
  > 
  > dataset <- do.call(
  +   cbind,
  +   c(sapply(paste0("col", 1:6), function(x) {
  +     rnorm(n = 500)
  +     },
  +     USE.NAMES = TRUE,
  +     simplify = FALSE
  +    ),
  +    list(target = sample(0:1, 500, TRUE))
  + ))
  > 
  > fold_list <- splitTools::create_folds(
  +   y = dataset[, 7],
  +   k = 3,
  +   type = "stratified",
  +   seed = 123
  + )
  > 
  > cv <- MLCrossValidation$new(
  +   learner = LearnerKnn$new(),
  +   fold_list = fold_list,
  +   seed = 123,
  +   ncores = 2
  + )
  Error: Package "class" must be installed to use 'learner = "LearnerKnn"'.
  Execution halted