java.lang.NoSuchMethodError: rx.subjects.PublishSubject.toSerialized()Lrx/subjects/SerializedSubject;

public class MyFirstRxVerticle extends AbstractVerticle {
Bucket bucket = null;

public static void main(String[] args) throws IOException {
    Launcher.executeCommand ( "run" , MyFirstRxVerticle.class.getName ( ) );
}


@Override
public void start(io.vertx.core.Future<Void> fut) throws IOException {

    System.out.println ( "-------------------------------" );
    CouchbaseEnvironment env = DefaultCouchbaseEnvironment.builder ( )
            //this set the IO socket timeout globally, to 45s
            .socketConnectTimeout ( ( int ) TimeUnit.SECONDS.toMillis ( 10000 ) )
            //this sets the connection timeout for openBucket calls globally (unless a particular call provides its own timeout)
            .connectTimeout ( TimeUnit.SECONDS.toMillis ( 12000 ) )
            .build ( );
    Cluster cluster = CouchbaseCluster.create ( env , "http://127.0.0.1:8091" );
    bucket = cluster.openBucket ( "default" , "" );
    System.out.println ( "bucket open........" );.....

this is my code where i got the error on " Cluster cluster = CouchbaseCluster.create ( env , “http://127.0.0.1:8091” )"-----
error is…

java.lang.NoSuchMethodError: rx.subjects.PublishSubject.toSerialized()Lrx/subjects/SerializedSubject;
at com.couchbase.client.core.event.DefaultEventBus.(DefaultEventBus.java:39)
at com.couchbase.client.core.env.DefaultCoreEnvironment.(DefaultCoreEnvironment.java:316)
at com.couchbase.client.java.env.DefaultCouchbaseEnvironment.(DefaultCouchbaseEnvironment.java:128)
at com.couchbase.client.java.env.DefaultCouchbaseEnvironment.(DefaultCouchbaseEnvironment.java:52)
at com.couchbase.client.java.env.DefaultCouchbaseEnvironment$Builder.build(DefaultCouchbaseEnvironment.java:510)
at MyFirstRxVerticle.start(MyFirstRxVerticle.java:195)
at io.vertx.core.impl.DeploymentManager.lambda$doDeploy$10(DeploymentManager.java:481)
at io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:344)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)