@Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Op that = (Op) o;
            return Objects.equals(key, that.key) && Objects.equals(value, that.value);
        }
@return if set then the existing value is updated,
        otherwise if null, the existing value is cleared
clients/src/main/java/org/apache/kafka/common/quota/ClientQuotaAlteration.java