There appears to be a disconnect between the API [1] and the implementation [2] of checkAndPut() regarding the expected value parameter when the caller wants to make the put conditional on the row not existing. The javadoc states that the caller should use a null expected value for this purpose, whereas the implementation is checking for a 0-length byte[]. If a null expected value is given, checkAndPut() will NPE; see HRegion.java:1520 in trunk.
I believe that null, rather than 0-length byte[], should be used for requiring row non-existence in checkAndPut(). Besides seeming like the right API, a 0-length byte[] is technically a valid row key (and least for a little put/get test I did; I found this surprising). Thoughts? john [1] http://hbase.apache.org/docs/r0.89.20100726/apidocs/org/apache/hadoop/hbase/ipc/HRegionInterface.html#checkAndPut(byte[], byte[], byte[], byte[], byte[], org.apache.hadoop.hbase.client.Put) [2] http://svn.apache.org/viewvc/hbase/trunk/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java?view=markup -- line 1520
