Set modifiable List to fields in var-args mutator method for model of List to enable the fields to mutate

The var-args mutator for some models whose type is List sets Unmodifiable List(jva.util.Arrays$ArrayList) to the field like the following.

/**
 * The handlers associated with the root logger.
 */
@SuppressWarnings("unchecked")
public T handlers(String... args) {
  handlers(Arrays.asList(args));
  return (T) this;
}

If the field(in this case, handlers) initialize as java.util.Arrays$ArrayList, we can't add elements to the field.