I dont get .doOnError clause get called when the document does not exist

From what I understand, if the document does not exist, I get the result back as an error.
But I dont see that .doOnError gets called. It always throw the exception instead
Am I doing something wrong here?
The code is below:

public static String readbucket(final String documnetId) {
    if (couchbase == null) {
        couchbase = new Couchbase(); 
    final Bucket bucket = couchbase.getNGTVEHDATABucket();
    JsonDocument result =null;
    try {
        result = (JsonDocument) bucket
            .doOnError(new Action1<Throwable>() {
                    public void call(Throwable throwable) {
                        logger.debug("Error reading the doucment : " + throwable.getLocalizedMessage());
            .timeout(1, TimeUnit.SECONDS) // don't forget the timeout
    } catch (Exception e) {
        // when the item does not exist, it always come here.
        logger.info("READ CB Exception  :" + e.getLocalizedMessage());
    return result.content().toString();