Self-Closing XML Tags and Empty Elements

Self-closing tags (empty elements) in XML represent elements with no content. They are shorthand for an open-close tag pair with nothing between them, and their JSON mapping requires careful consideration.

XML with self-closing tags:

<user>
  <name>Alice</name>
  <email>alice@example.com</email>
  <phone/>
  <avatar></avatar>
  <bio/>
  <settings enabled="true"/>
</user>

Note: <phone/> and <phone></phone> are semantically identical in XML.

JSON conversion options:

Option 1: Map to null

{
  "user": {
    "name": "Alice",
    "email": "alice@example.com",
    "phone": null,
    "avatar": null,
    "bio": null,
    "settings": { "@enabled": "true" }
  }
}

Option 2: Map to empty string

{
  "user": {
    "name": "Alice",
    "email": "alice@example.com",
    "phone": "",
    "avatar": "",
    "bio": "",
    "settings": { "@enabled": "true" }
  }
}

Option 3: Map to empty object

{
  "user": {
    "phone": {},
    "settings": { "@enabled": "true" }
  }
}

Which option to choose:

Scenario	Best mapping	Reason
Field is optional/absent	null	Semantically represents "no value"
Field expects text but is empty	""	Preserves the field with empty content
Element may have attributes	{}	Allows attribute keys alongside content
Element with attributes only	{ "@attr": "val" }	Preserves attribute data

Self-closing tags with attributes are a special case. <settings enabled="true"/> has no text content but does have an attribute. In JSON:

{ "settings": { "@enabled": "true" } }

When converting JSON to XML:

JSON value	XML output
null	<field/> or <field xsi:nil="true"/>
""	<field></field> or <field/>
{}	<field/>

The distinction between null, empty string, and empty object in JSON all collapse to the same self-closing tag in XML. This is one of the areas where round-trip conversion can lose information.

Best practice: Use null for empty elements when converting XML to JSON, unless the consuming code specifically needs empty strings. Document the convention so consumers know how to interpret null values.