can't iterate consumed messages when checking errorCode first

Hi all,

I'm using Kafka low level consumer api and find in the below codes
"iterator.hasNext" always return false. Through debugging, I'm sure the
messageSet has the size of "fetchSize"

* val consumer = new SimpleConsumer(broker.host, broker.port,
soTimeout, soBufferSize, clientId)*
* val request = new FetchRequestBuilder()*
* .addFetch(topic, partition, offset, fetchSize)*
* .build()*
* val response = consumer.fetch(request)*
* response.errorCode(topic, partition) match {*
* case NoError => {*
* iterator = response.messageSet(topic, partition).iterator*
* }*
* case error => throw exceptionFor(error)*
* }*

The weird thing is that the iterator works fine when I get iterator
directly without checking the error code.

* val consumer = new SimpleConsumer(broker.host, broker.port,
soTimeout, soBufferSize, clientId)*
* val request = new FetchRequestBuilder()*
* .addFetch(topic, partition, offset, fetchSize)*
* .build()*
* consumer.fetch(request).messageSet(topic, partition).iterator*

Any thoughts ?

Thanks,
Manu Zhang