Package check result: ERROR

Check: examples, Result: ERROR
  Running examples in ‘mlr3fairness-Ex.R’ failed
  The error most likely occurred in:
  
  > base::assign(".ptime", proc.time(), pos = "CheckExEnv")
  > ### Name: MeasureFairness
  > ### Title: Base Measure for Fairness
  > ### Aliases: MeasureFairness
  > 
  > ### ** Examples
  > 
  > library("mlr3")
  > # Create MeasureFairness to measure the Predictive Parity.
  > t = tsk("adult_train")
  > learner = lrn("classif.rpart", cp = .01)
  Warning: Package 'rpart' required but not installed for Learner 'classif.rpart'
  > learner$train(t)
  Error: The following packages could not be loaded: rpart
  Execution halted