When reporting a mismatch on data between objects in 11g, null elements are missing (not shown at all).
On 12c however they are showing as <attribute_name/> - that is empty XML tag.
If we figure out how to resolve this, we should make it consistent across db versions.
Example:

create or replace type test_dummy_object as object (
  id number,
  "name"  varchar2(30),
  "Value" varchar2(30)
)
/

select xmltype.createXml( test_dummy_object(null, null, null) ) from dual ;

On 11g

<TEST_DUMMY_OBJECT/>

On 12c

<TEST_DUMMY_OBJECT><ID/>
<name/>
<Value/>
</TEST_DUMMY_OBJECT>