Named getter of HTMLAllCollection etc should be nullable

LayoutTests/fast/dom/html-collections-named-getter-expected.txt

 This tests verifies that namedItem and named getter returns the first matched item for all but all, options, and form controls collections.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 document.all
 PASS document.all instanceof HTMLAllCollection is true
 FAIL document.all instanceof HTMLCollection should be true. Was false.
 PASS initialLength = document.all.length; elements = [insertElementWithId('b', 'foo'), insertElementWithId('q', 'foo')];
      document.all.length is initialLength + 2;
 PASS document.all['foo'].length is 2
 PASS document.all['foo'][0] is elements[0]
 PASS document.all['foo'][1] is elements[1]
 PASS elements[0].parentNode.removeChild(elements[0]); document.all['foo'] is elements[1]
+PASS document.all['no-such-element'] is undefined.
 
 form.elements
 PASS form.elements instanceof HTMLFormControlsCollection is true
 PASS form.elements instanceof HTMLCollection is true
 PASS form.elements.length is 0
 PASS elements = [createElementWithId('input', 'foo'), createElementWithId('input', 'foo')];
      form.appendChild(elements[0]); form.elements.length is 1
 PASS form.elements['foo'] is elements[0]
 PASS form.appendChild(elements[1]); form.elements.length is 2
 PASS form.elements['foo'].toString() is '[object RadioNodeList]'
 PASS form.elements['foo'].length is 2
 PASS form.elements['foo'][0] is elements[0]
 PASS form.elements['foo'][1] is elements[1]
 PASS form.removeChild(elements[0]); form.elements['foo'] is elements[1]
 PASS removeTestElements(); form.elements.length is 0
+PASS form.elements['no-such-element'] is undefined.
 
 select.options
 PASS form.appendChild(createElementWithId('select', 'bar')); form.elements.length is 1
 PASS select = form.elements[0]; select.options instanceof HTMLOptionsCollection is true
 PASS select.options instanceof HTMLCollection is true
 PASS select.options.length is 0
 PASS elements = [createElementWithId('option', 'foo'), createElementWithId('option', 'foo')];
      select.appendChild(elements[0]); select.options.length is 1
 PASS select.options['foo'] is elements[0]
 PASS select.appendChild(elements[1]); select.options.length is 2
 PASS select.options['foo'].toString() is '[object NodeList]'
 PASS select.options['foo'].length is 2
 PASS select.options['foo'][0] is elements[0]
 PASS select.options['foo'][1] is elements[1]
 PASS select.removeChild(elements[0]); select.options['foo'] is elements[1]
 PASS select.innerHTML = ''; select.options.length is 0
 PASS removeTestElements(); form.elements.length is 0
+PASS select.options['no-such-element'] is undefined.
 
 document.images
 PASS document.images.length is 0
 PASS elements[0] = insertElementWithId('img', 'foo'); document.images.length is 1
 PASS elements[1] = insertElementWithId('img', 'foo'); document.images.length is 2
 PASS document.images['foo'] is elements[0]
 PASS removeTestElements(); document.images.length is 0
 
 document.applets
 PASS document.applets.length is 0
@@ skipping 35 matching lines @@
 PASS document.scripts.length is 2
 PASS elements[0] = insertElementWithId('script', 'foo'); document.scripts.length is 3
 PASS elements[1] = insertElementWithId('script', 'foo'); document.scripts.length is 4
 PASS document.scripts['foo'] is elements[0]
 PASS removeTestElements(); document.scripts.length is 2
 
 PASS successfullyParsed is true
 
 TEST COMPLETE