Returns {@code true} if this immutable range set's implementation contains references to
   * user-created objects that aren't accessible via this range set's methods. This is generally
   * used to determine whether {@code copyOf} implementations should make an explicit copy to avoid
   * memory leaks.
Returns {@code true} if this immutable range set's implementation contains references to
   * user-created objects that aren't accessible via this range set's methods. This is generally
   * used to determine whether {@code copyOf} implementations should make an explicit copy to avoid
   * memory leaks. | ImmutableRangeSet.java