core: Fixed #2600: jQuery.extend no longer skips over null properties.

src/core.js

@@ -587,7 +587,7 @@ jQuery.extend = jQuery.fn.extend = function() {
 					target[ name ] = jQuery.extend( deep, src, copy );
 
 				// Don't bring in undefined values
-				else if ( copy != undefined )
+				else if ( copy !== undefined )
 					target[ name ] = copy;
 
 			}

test/unit/core.js

@@ -1025,7 +1025,7 @@ test("is(String)", function() {
 });
 
 test("$.extend(Object, Object)", function() {
-	expect(17);
+	expect(20);
 
 	var settings = { xnumber1: 5, xnumber2: 7, xstring1: "peter", xstring2: "pan" },
 		options = { xnumber2: 1, xstring2: "x", xxx: "newstring" },
@@ -1049,7 +1049,17 @@ test("$.extend(Object, Object)", function() {
 	isObj( deep1.foo, deepmerged.foo, "Check if foo: settings must be extended" );
 	isObj( deep2.foo, deep2copy.foo, "Check if not deep2: options must not be modified" );
 	equals( deep1.foo2, document, "Make sure that a deep clone was not attempted on the document" );
-
+	
+	var nullUndef;
+	nullUndef = jQuery.extend({}, options, { xnumber2: null });
+	ok( nullUndef.xnumber2 === null, "Check to make sure null values are copied");
+	
+	nullUndef = jQuery.extend({}, options, { xnumber2: undefined });
+	ok( nullUndef.xnumber2 === options.xnumber2, "Check to make sure undefined values are not copied");
+	
+	nullUndef = jQuery.extend({}, options, { xnumber0: null });
+	ok( nullUndef.xnumber0 === null, "Check to make sure null values are inserted");
+	
 	var target = {};
 	var recursive = { foo:target, bar:5 };
 	jQuery.extend(true, target, recursive);