code: public final void addAllValues(@NonNull final Collection<String> values) {
          Condition.INSTANCE.ensureNotNull(values, "The values may not be null");
  
          if (this.values != null) {
              if (this.values.addAll(values)) {
                  if (persistSet(this.values)) {
                      notifyChanged();
                  }
              }
          } else {
              Set<String> newValues = new HashSet<>(values);
              setValues(newValues);
          }
      }
docs: Adds all values, which are contained by a specific collection, to the preference. By adding
  values, the changes will be persisted.
  
  @param values
  A collection, which contains the values, which should be added, as an instance of the
  type {@link Collection} or an empty collection, if no values should be added