private static final Pattern USERNAME_PATTERN = Pattern.compile("\\w+");

        /**
         * Validates the excludeUsers field
         */
        public FormValidation doCheckExcludedUsers(@QueryParameter String value) throws IOException, ServletException {
            for (String user : Util.fixNull(value).trim().split("[\\r\\n]+")) {
                user = user.trim();

                if ("".equals(user)) {
                    continue;
                }

                if (!USERNAME_PATTERN.matcher(user).matches()) {
                    return FormValidation.error("Invalid username: " + user);
                }
            }

            return FormValidation.ok();
        }