System.clearProperty("123");
        System.clearProperty("test_var");
    }

    public void test_resolve_edgeCases() {
        // Test empty property replacement
        System.setProperty("empty", "");
        String value = "${empty}";
        assertEquals("", ResourceUtil.resolve(value));

        // Test property with just spaces
        System.setProperty("spaces", "   ");

    }

    /**
     * Returns the resource from the context class loader.
     *
     * @param path
     *            The resource path. Must not be {@literal null} or empty string.
     * @return The resource {@link URL}
     * @see #getResource(String, String)
     */
    public static URL getResource(final String path) {
        assertArgumentNotEmpty("path", path);

            }

            @Override
            protected String getClientIp() {
                return StringUtil.EMPTY;
            }
        };
    }

    public void test_login() {
        activityHelper.useEcsFormat = false;
        activityHelper.login(OptionalThing.empty());
        assertEquals("action:LOGIN\tuser:-\tpermissions:-", localLogMsg.get());

     *
     * @param date the date to format
     * @return formatted date string, or empty string if date is null
     */
    public static String formatDate(final Date date) {
        if (date == null) {
            return StringUtil.EMPTY;
        }
        final SimpleDateFormat sdf = new SimpleDateFormat(Constants.ISO_DATETIME_FORMAT);

    }

    /**
     * Returns the bundle. Returns <code>null</code> if not found.
     *
     * @param name the resource bundle name (must not be {@literal null} or empty)
     * @param locale the locale
     * @param classLoader the class loader (must not be {@literal null} or empty)
     * @return {@link ResourceBundle}
     * @see ResourceBundle#getBundle(String, Locale, ClassLoader)
     */

     *
     * @param pattern
     *            The date pattern. Must not be {@literal null} or an empty string.
     * @param propertyNames
     *            An array of property names. Each element must not be {@literal null} or an empty string.
     * @return A {@link CopyOptions} with a date converter applied.
     * @see CopyOptions#dateConverter(String, CharSequence...)

     * Processes collection definitions and tracks the element hierarchy.
     *
     * @param uri the namespace URI, or empty string if none
     * @param localName the local name without prefix, or empty string if namespace processing is not performed
     * @param qName the qualified name with prefix, or empty string if qualified names are not available
     * @param attributes the attributes attached to the element

     *
     * @param u the URL string to extract host from
     * @return the host name, or empty string if URL is blank, or unknown hostname if parsing fails
     */
    default String getHost(final String u) {
        if (StringUtil.isBlank(u)) {
            return StringUtil.EMPTY; // empty
        }

        String url = u;
        final String originalUrl = url;

        int idx = url.indexOf("://");

     *
     * @return the application type string, or empty string if not set
     */
    public static String getAppType() {
        final String appType = System.getenv(FESS_APP_TYPE);
        if (StringUtil.isNotBlank(appType)) {
            return appType;
        }
        return StringUtil.EMPTY;
    }

    /**

   * otherwise returns an empty stream.
   */
  public static <T> Stream<T> stream(com.google.common.base.Optional<T> optional) {
    return optional.isPresent() ? Stream.of(optional.get()) : Stream.empty();
  }

  /**
   * If a value is present in {@code optional}, returns a stream containing only that element,
   * otherwise returns an empty stream.
   *