Trying to add CamundaMap extension programmatically

I’m trying to add CamundaMap extension programmatically, but the extension doesn’t appear in the XML.

Code:

ServiceTask task = CamundaBuilder.createElement(modelInstance, process, ServiceTask.class, ACTIVITY_1);
task.setCamundaDelegateExpression(ACTIVITY_IMPL);

    ExtensionElements extensionElements = task.getExtensionElements();
    if (extensionElements == null) {
        extensionElements = modelInstance.newInstance(ExtensionElements.class);
        task.setExtensionElements(extensionElements);
    }

    CamundaEntry entry = modelInstance.newInstance(CamundaEntry.class);
    entry.setCamundaKey("key");
    entry.setTextContent("value");

    CamundaMap map = modelInstance.newInstance(CamundaMap.class);
    map.addChildElement(entry);

    CamundaInputParameter inputParameter = modelInstance.newInstance(CamundaInputParameter.class);
    inputParameter.setCamundaName("inputParameter");
    inputParameter.setValue(map);

    CamundaInputOutput inputOutput = modelInstance.newInstance(CamundaInputOutput.class);
    inputOutput.addChildElement(inputParameter);

    extensionElements.getElements().add(inputOutput);

Thanks for your time.