What is the correct way to represent null XML elements?

What is the correct way to represent null XML elements?

xml null xml-nil

xml

What does i:nil="true" mean?

xml null xml-nil

xml

Selecting null value from XML in SQL Server

sql-server xml null xml-nil

xml

XML, what is this: null or empty element?

xml xsd null dtd xmlserializer

xml

Getting document as null [#document: null] After parsing XML in java using DocumentBuilder

xml null document

xml