@Override
        public void ensureValid(String name, Object o) {
            String s = (String) o;
            if (s != null && s.isEmpty()) {
                throw new ConfigException(name, o, "String must be non-empty");
            }
        }
A numeric range that checks both the upper (inclusive) and lower bound
clients/src/main/java/org/apache/kafka/common/config/ConfigDef.java