Vert.x RabbitMQ encode NullPointerException

I am working with Java8 in Vert.x 3.9.2 and vertx-rabbitmq-client same version. I am trying to publish a message to an exchange, but regardless the configuration the exchange has (topic/fanout) the same exception is thrown:

 java.lang.NullPointerException
        at io.vertx.rabbitmq.impl.Utils.encode(Utils.java:179)
        at io.vertx.rabbitmq.impl.RabbitMQClientImpl.lambda$basicPublish$8(RabbitMQClientImpl.java:213)
        at io.vertx.rabbitmq.impl.RabbitMQClientImpl.lambda$forChannel$34(RabbitMQClientImpl.java:488)
        at io.vertx.core.impl.ContextImpl.lambda$executeBlocking$2(ContextImpl.java:313)
        at io.vertx.core.impl.TaskQueue.run(TaskQueue.java:76)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
        at java.base/java.lang.Thread.run(Thread.java:834)

This is my code:

          amqpClient
             .exchangeDeclare(
                "orders", // name
                "topic", // type
                true, //durable
                false, //autodelete 
                exchangeDeclareResult -> {
                    if (exchangeDeclareResult.succeeded()) {
                        amqpClient
                            .basicPublish(
                                "orders", 
                                "test",
                                new JsonObject()..... // Another properties
                                publishResult -> {
                                    if (publishResult.succeeded())
                                        mainPromise.complete();
                                    else {
                                        publishResult.cause().printStackTrace();
                                        mainPromise.fail(publishResult.cause());
                                    }
                                });
                    } 
                    else
                        mainPromise.fail(exchangeDeclareResult.cause());
                }
            );

I think the problem is about json content serialization. Every property in my body has content, I mean there is no null values. An aditional issue I can notice is a message in the exception during debug:

NullPointerException@91 "java.lang.NullPointerException"
cause: NullPointerException@91 "java.lang.NullPointerException"
depth:9
backtrace Object[5]@99
stackTraceElement[9]@133
suppressedExceptions: Collections$EmptyList@101 size=0

Thanks in advance.

Does the new JsonObject()... // Another properties object have a body property that has a string value? That is what basicPulish is extracting from the message. Note that not having a property might return null. So it isn't sufficient if all of your properties have non-null values, you should also have all required properties