Returns “NULL” if the task is not of type “costsens”.
getTaskCosts(task, subset = NULL)(CostSensTask) The task.
(matrix | NULL).
Other task: getTaskClassLevels,
  getTaskData, getTaskDesc,
  getTaskFeatureNames,
  getTaskFormula, getTaskId,
  getTaskNFeats, getTaskSize,
  getTaskTargetNames,
  getTaskTargets, getTaskType,
  subsetTask