@Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Map.Entry<String, String> entry : entries()) {
            sb.append(entry.getKey());
            if (!Strings.isNullOrEmpty(entry.getValue())) {
                sb.append('=');
                sb.append(entry.getValue());
            }
            sb.append('&');
        }

        // Remove trailing '&'.
        if (!sb.isEmpty() && sb.charAt(sb.length() - 1) == '&') {
            sb.deleteCharAt(sb.length() - 1);
        }
        return sb.toString();
    }
Replace any/all entries with this key, with this single entry.
zuul-core/src/main/java/com/netflix/zuul/message/http/HttpQueryParams.java