Completed Tasks are not returned

Summary

function listTasks(taskListId) {
  try {
    // List the task items of specified tasklist using taskList id.
    const tasks = Tasks.Tasks.list(taskListId);
    // Tasks.Tasks.list({tasklist: tasklistId, showCompleted: true, completedMin: '1970-01-01T00:00:00Z'});
    // If tasks are available then print all task of given tasklists.
    if (!tasks.items) {
      console.log('No tasks found.');
      return;
    }
    // Print the task title and task id of specified tasklist.
    for (let i = 0; i < tasks.items.length; i++) {
      const task = tasks.items[i];
      console.log('Task with title "%s" and ID "%s" was found.', task.title, task.id);
    }
  } catch (err) {
    // TODO (developer) - Handle exception from Task API
    console.log('Failed with an error %s', err.message);
  }
}

Expected Behavior

Logging all the tasks

Actual Behavior

It only returns the uncompleted tasks. I want to return all the tasks of a list.

Steps to Reproduce the Problem

Just run it in Google Apps Scripts with the list ID.