convert xml to json

json4s version

3.7.0-M4

scala version

2.12.10

jdk version

1.8

I have one xml just like:

<Teacher id="1">
    <name>Jim</name>
    <contact phone="123456" id="2">
        <color>blue</color>
    </contact>
</Teacher>

When I convert this xml to json, it looks nice:
{"Teacher":{"id":"1","name":"Jim","contact":{"phone":"123456","id":"2","color":"blue"}}}

But if I remove the "color" tag, just like:

<Teacher id="1">
    <name>Jim</name>
    <contact phone="123456" id="2"></contact>
</Teacher>

It would get this json result:
{"Teacher":{"id":"1","name":"Jim","phone":"123456","id":"2"}}
actually I think the "contact" tag should be Map structure

Reproduce the XML-to-JSON conversion with the two examples in the issue, then trace the json4s XML conversion entry point to see how an empty contact element is handled. Done means the contact element remains a nested map when it has attributes but no child elements, with tests covering both examples.