Fixes #9104 again.

Author: jaubourg

src/deferred.js

@@ -50,7 +50,7 @@ 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, newDefer.ping );
 									} else {
 										newDefer[ action ]( returned );