class StringUtils {

    private StringUtils() {}

    public static boolean isNullOrEmpty(String str) {
        return (str == null) || str.isEmpty();
    }

    public static boolean isNotNullOrEmpty(String str) {
        return !isNullOrEmpty(str);
    }

    /**
     * Format the string. Replace "{}" with %s and format the string using {@link String#format(String, Object...)}.
     */
    public static String format(String str, Object... args) {
        str = str.replaceAll("\\{}", "%s");

        return String.format(str, args);
    }

    /**
     * <p>Adds a substring only if the source string does not already start with the substring,
     * otherwise returns the source string.</p>
     * <p/>
     * <p>A {@code null} source string will return {@code null}.
     * An empty ("") source string will return the empty string.
     * A {@code null} search string will return the source string.</p>
     * <p/>
     * <pre>
     * StringUtils.addStart(null, *)      = *
     * StringUtils.addStart("", *)        = *
     * StringUtils.addStart(*, null)      = *
     * StringUtils.addStart("domain.com", "www.")  = "www.domain.com"
     * StringUtils.addStart("abc123", "abc")    = "abc123"
     * </pre>
     *
     * @param str the source String to search, may be null
     * @param add the String to search for and add, may be null
     * @return the substring with the string added if required
     */
    public static String addStart(String str, String add) {<FILL_FUNCTION_BODY>}

}

        if (isNullOrEmpty(add)) {
            return str;
        }

        if (isNullOrEmpty(str)) {
            return add;
        }

        if (!str.startsWith(add)) {
            return add + str;
        }

        return str;
    
<no_super_class>