/**
     * Expands a version range to a list of matching versions, in ascending order.
     * For example, resolves "[3.8,4.0)" to "3.8", "3.8.1", "3.8.2".
     * The returned list of versions is only dependent on the configured repositories and their contents.
     * The supplied request may also refer to a single concrete version rather than a version range.

  }

  /**
   * Returns an immutable range set containing the specified single range. If {@link Range#isEmpty()
   * range.isEmpty()}, this is equivalent to {@link ImmutableRangeSet#of()}.
   */
  public static <C extends Comparable> ImmutableRangeSet<C> of(Range<C> range) {
    checkNotNull(range);
    if (range.isEmpty()) {
      return of();
    } else if (range.equals(Range.all())) {
      return all();
    } else {

      return null;
    } else {
      Range<K> range = ranges.get(index);
      return range.contains(key) ? Maps.immutableEntry(range, values.get(index)) : null;
    }
  }

  @Override
  public Range<K> span() {
    if (ranges.isEmpty()) {
      throw new NoSuchElementException();
    }
    Range<K> firstRange = ranges.get(0);
    Range<K> lastRange = ranges.get(ranges.size() - 1);