code: private void addActivityWithDataUsage(String activity) {
          Validate.notNull(activity);
          Validate.notEmpty(activity);
          Set<String> currentActivities = getActivitiesWithDataUsage();
          currentActivities.add(activity);
          setProperty(ProcessContextProperty.ACTIVITIES_WITH_DATA_USAGE, ArrayUtils.toString(currentActivities.toArray()));
      }
docs: Adds an activity to the list of activities with data usage.
  
  @param activity The name of the activity to add.
  @throws ParameterException if the activity name is invalid.