xsi:nil is not honored by xmltable

If an element is returnable by xmltable, but marked as nil more than likely an exception will be produced when attempting to convert the empty string value to a result.

For example:

select * from xmltable('/a/b' passing convert('<a xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><b xsi:nil="true"/><b>1</b></a>', xml) columns val integer path '.') as x

will error converting the first b element to an integer.