Update/remove a field document

Elastic Stack Elasticsearch
1

Imagine a class as:

class DummyClass
{
    String field1;
    String field2;
}

I'm able to create an DummyClass object and save it on ES:

DummyClass dummy = new DummyClass();
dummy.field1 = "sample1";
dummy.field2 = "sample2";

byte[] source = this.jacksonMapper.writeValueAsBytes(dummy);
this.elasticsearchResources.getElasticsearchClient()
    .prepareIndex()
	.setIndex("index")
	.setType("type")
	.setSource(source)
    .request();

source's content is:

{
    "field1": "sample1",
    "field2": "sample2"
}

So, I need to do a change like: dummy.field1 = null, so I need field1 is deleted (I don't want ES set field1 = null).

So, I've tried this:

 dummy.field1 = null;

 byte[] source = this.jacksonMapper.writeValueAsBytes(dummy);

 this.elasticsearchResources.getElasticsearchClient()
		.prepareUpdate()
		.setIndex("index")
		.setType(type)
		.setId(id.toString())
		.setDoc(source)
		.setUpsert(source)
		.setDetectNoop(true)
        .request();

source's content is:

{
    "field2": "sample2"
}

After that, ES doesn't delete field1 from document.
I'm not quite able to figure out what I'm doing wrong.