if( threadLocalOutputStreams == null || threadLocalOutputStreams.isEmpty() )
return null;
final OutputMergeTask outputMergeTask = new OutputMergeTask();
for( Map.Entry<Stub,Storage> entry: threadLocalOutputStreams.entrySet() ) {
final Stub stub = entry.getKey();
final Storage storageEntry = entry.getValue();
storageEntry.close();
outputMergeTask.addMergeOperation(getTargetStream(stub), storageEntry);
}