*
     * @param o
     *            object to be removed from this set, if present.
     * @return true if the set contained the specified element.
     */
    @Override
    public boolean remove(final Object o) {
        return map.remove(o) == PRESENT;
    }

    /**
     * Removes all of the elements from this set.
     */
    @Override
    public void clear() {
        map.clear();
    }

        return map.containsKey(o);
    }

    @Override
    public boolean add(final String o) {
        return map.put(o, PRESENT) == null;
    }

    @Override
    public boolean remove(final Object o) {
        return map.remove(o) == PRESENT;
    }

    @Override
    public void clear() {
        map.clear();
    }

    /**
     * {@link InputStream}をリセットします。
     *
     * @param is
     *            入力ストリーム。{@literal null}であってはいけません
     * @see InputStream#reset()
     */
    public static void reset(final InputStream is) {
        assertArgumentNotNull("is", is);

        try {
            is.reset();
        } catch (final IOException e) {
            throw new IORuntimeException(e);
        }
    }