Make nullable DOMString always treat undefined as null

third_party/WebKit/LayoutTests/imported/web-platform-tests/dom/nodes/attributes-expected.txt

 This is a testharness.js-based test.
 FAIL AttrExodus assert_false: should not be a Node expected false got true
 PASS When qualifiedName does not match the Name production, an INVALID_CHARACTER_ERR exception is to be thrown. (setAttribute) 
 PASS setAttribute should lowercase its name argument (upper case attribute) 
 PASS setAttribute should lowercase its name argument (mixed case attribute) 
 PASS setAttribute should not throw even when qualifiedName starts with 'xmlns' 
 PASS Basic functionality should be intact. 
 PASS setAttribute should not change the order of previously set attributes. 
 PASS setAttribute should set the first attribute with the given name 
 PASS setAttribute should set the attribute with the given qualified name 
@@ skipping 15 matching lines @@
 PASS Attribute values should not be parsed. 
 PASS Specified attributes should be accessible. 
 PASS Entities in attributes should have been expanded while parsing. 
 PASS Unset attributes return null 
 PASS First set attribute is returned by getAttribute 
 PASS Style attributes are not normalized 
 FAIL Only lowercase attributes are returned on HTML elements (upper case attribute) assert_equals: expected (object) null but got (string) "left"
 FAIL Only lowercase attributes are returned on HTML elements (mixed case attribute) assert_equals: expected (object) null but got (string) "tasty"
 PASS First set attribute is returned with mapped attribute set first 
 PASS First set attribute is returned with mapped attribute set later 
-FAIL Non-HTML element with upper-case attribute assert_equals: el.hasAttributeNS(undefined) expected true but got false
+PASS Non-HTML element with upper-case attribute 
 PASS Attribute with prefix in local name 
 PASS Attribute loses its owner when removed 
 PASS Basic functionality of getAttributeNode/getAttributeNodeNS 
 PASS Basic functionality of setAttributeNode 
 PASS Basic functionality of setAttributeNodeNS 
 PASS If attr’s element is neither null nor element, throw an InUseAttributeError. 
 PASS Replacing an attr by itself 
 PASS Basic functionality of removeAttributeNode 
 PASS setAttributeNode on bound attribute should throw InUseAttributeError 
 PASS setAttributeNode, if it fires mutation events, should fire one with the new node when resetting an existing attribute 
 PASS setAttributeNode, if it fires mutation events, should fire one with the new node when resetting an existing attribute (outer shell) 
 PASS setAttributeNode called with an Attr that has the same name as an existing one should not change attribute order 
 FAIL getAttributeNames tests el.getAttributeNames is not a function
 FAIL Own property correctness with basic attributes assert_array_equals: lengths differ, expected 2 got 0
 FAIL Own property correctness with non-namespaced attribute before same-name namespaced one assert_array_equals: lengths differ, expected 3 got 0
 FAIL Own property correctness with namespaced attribute before same-name non-namespaced one assert_array_equals: lengths differ, expected 3 got 0
 FAIL Own property correctness with two namespaced attributes with the same name-with-prefix assert_array_equals: lengths differ, expected 3 got 0
 FAIL Own property names should only include all-lowercase qualified names for an HTML element in an HTML document assert_array_equals: lengths differ, expected 8 got 6
 FAIL Own property names should include all qualified names for a non-HTML element in an HTML document assert_array_equals: lengths differ, expected 12 got 6
 FAIL Own property names should include all qualified names for an HTML element in a non-HTML document assert_array_equals: lengths differ, expected 12 got 6
 Harness: the test ran to completion.