Fixes #9104. Returning null or undefined in a pipe callback shouldn't end up...

Fixes #9104. Returning null or undefined in a pipe callback shouldn't end up throwing an exception. Silly, silly, me.

src/deferred.js

@@ -119,7 +119,7 @@ jQuery.extend({
 						if ( jQuery.isFunction( fn ) ) {
 							deferred[ handler ](function() {
 								returned = fn.apply( this, arguments );
-								if ( jQuery.isFunction( returned.promise ) ) {
+								if ( returned && jQuery.isFunction( returned.promise ) ) {
 									returned.promise().then( newDefer.resolve, newDefer.reject );
 								} else {
 									newDefer[ action ]( returned );

test/unit/deferred.js

@@ -145,7 +145,7 @@ jQuery.each( [ "", " - new operator" ], function( _, withNew ) {
 
 test( "jQuery.Deferred.pipe - filtering (done)", function() {
 
-	expect(3);
+	expect(4);
 
 	var defer = jQuery.Deferred(),
 		piped = defer.pipe(function( a, b ) {
@@ -173,11 +173,15 @@ test( "jQuery.Deferred.pipe - filtering (done)", function() {
 	jQuery.Deferred().reject().pipe(function() {
 		ok( false, "pipe should not be called on reject" );
 	});
+
+	jQuery.Deferred().resolve().pipe( jQuery.noop ).done(function( value ) {
+		strictEqual( value, undefined, "pipe done callback can return undefined/null" );
+	});
 });
 
 test( "jQuery.Deferred.pipe - filtering (fail)", function() {
 
-	expect(3);
+	expect(4);
 
 	var defer = jQuery.Deferred(),
 		piped = defer.pipe( null, function( a, b ) {
@@ -205,6 +209,10 @@ test( "jQuery.Deferred.pipe - filtering (fail)", function() {
 	jQuery.Deferred().resolve().pipe( null, function() {
 		ok( false, "pipe should not be called on resolve" );
 	} );
+
+	jQuery.Deferred().reject().pipe( null, jQuery.noop ).fail(function( value ) {
+		strictEqual( value, undefined, "pipe fail callback can return undefined/null" );
+	});
 });
 
 test( "jQuery.Deferred.pipe - deferred (done)", function() {