Named getter of HTMLAllCollection etc should be nullable

Source/core/testing/UnionTypesTest.idl

Index: Source/core/testing/UnionTypesTest.idl
diff --git a/Source/core/testing/UnionTypesTest.idl b/Source/core/testing/UnionTypesTest.idl
index f3375202d1deacda8504db60588e0dc4c965f608..ddb08479d41404ff647b3fc19aed79a02e3ac83e 100644
--- a/Source/core/testing/UnionTypesTest.idl
+++ b/Source/core/testing/UnionTypesTest.idl
@@ -12,6 +12,10 @@
     [ImplementedAs=doubleOrStringArg] DOMString doubleOrStringDefaultDoubleArg(optional (double or DOMString) arg = 3.14);
     [ImplementedAs=doubleOrStringArg] DOMString doubleOrStringDefaultStringArg(optional (double or DOMString) arg = "foo");
     [ImplementedAs=doubleOrStringArg] DOMString doubleOrStringDefaultNullArg(optional (double or DOMString)? arg = null);
+
     DOMString doubleOrStringArrayArg((double or DOMString)[] arg);
     DOMString doubleOrStringSequenceArg(sequence<(double or DOMString)> arg);
+
+    DOMString nodeListOrElementArg((NodeList or Element) arg);
+    DOMString nodeListOrElementOrNullArg((NodeList or Element)? arg);
 };