Fix #14101: $().data() should be undefined, not null

- Backported 30eee925 for 1.x

src/data.js

@@ -272,8 +272,7 @@ jQuery.extend({
 
 jQuery.fn.extend({
 	data: function( key, value ) {
-		var i, name,
-			data = null,
+		var i, name, data,
 			elem = this[0],
 			attrs = elem && elem.attributes;
 
@@ -319,7 +318,7 @@ jQuery.fn.extend({
 
 			// Gets one value
 			// Try to fetch any internally stored data first
-			elem ? dataAttr( elem, key, jQuery.data( elem, key ) ) : null;
+			elem ? dataAttr( elem, key, jQuery.data( elem, key ) ) : undefined;
 	},
 
 	removeData: function( key ) {

test/unit/data.js

@@ -164,6 +164,12 @@ test("jQuery.acceptData", function() {
 	ok( !jQuery.acceptData( document.createTextNode("") ), "text" );
 });
 
+// attempting to access the data of an undefined jQuery element should be undefined
+test("jQuery().data() === undefined (#14101)", 2, function() {
+	strictEqual(jQuery().data(), undefined);
+	strictEqual(jQuery().data("key"), undefined);
+});
+
 test(".data()", function() {
 	expect(5);