class StrictStringValidator implements Setting.Validator<String> {

        private final String key;

        StrictStringValidator(String key) {
            this.key = key;
        }

        @Override
        public void validate(String value) {<FILL_FUNCTION_BODY>}
    }

            if (Booleans.isBoolean(value)) {
                throw new IllegalArgumentException(INVALID_MESSAGE + key + "'");
            }
            try {
                Long.parseLong(value);
                throw new IllegalArgumentException(INVALID_MESSAGE + key + "'");
            } catch (NumberFormatException e) {
                // pass, not a number
            }
        
<no_super_class>