cassandra hadoop reducer writing to CQL3 - primary key - must it be text type?

[John Lumby]

I have been expermimenting with using hadoop for a map/reduce operation on 
cassandra,
outputting to the CqlOutputFormat.class.
I based my first program fairly closely on the famous WordCount example in 
examples/hadoop_cql3_word_count
except  ---  I set my output colfamily to have a bigint primary key :

CREATE TABLE archive_recordids ( recordid bigint , count_num bigint, PRIMARY 
KEY (recordid))

and simply tried setting this key as one of the keys in the output 
            keys.put("recordid", ByteBufferUtil.bytes(recordid.longValue()));

but it always failed with a strange error :

java.io.IOException: InvalidRequestException(why:Key may not be empty)