public class DefaultMQPullConusmerImpl {
    // ...
    private void checkConfig() throws MQClientException {
        // because this method has check group not empty
        Validators.checkGroup(this.defaultMQPullConsumer.getConsumerGroup());

        // this check should be unnecessary
        if (null == this.defaultMQPullConsumer.getConsumerGroup()) {
            throw new MQClientException(
                "consumerGroup is null"
                    + FAQUrl.suggestTodo(FAQUrl.CLIENT_PARAMETER_CHECK_URL),
                null);
        }
        // ...
    }
    // ...
}

public class Validators {
    // ...
    public static void checkGroup(String group) throws MQClientException {
        // check group is not null or empty
        if (UtilAll.isBlank(group)) {
            throw new MQClientException("the specified group is blank", null);
        }
        // ...
    }
    // ...
}