bug #3551 [Cookbook][Dynamic Form Modification] Fix sample code (ryba…

…kit)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #3551).

Discussion
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[Cookbook][Dynamic Form Modification] Fix sample code

Commits
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0497b38 [Cookbook][Dynamic Form Modification] Fix sample code

cookbook/form/dynamic_form_modification.rst

@@ -123,7 +123,7 @@ the event listener might look like the following::
             // check if the Product object is "new"
             // If no data is passed to the form, the data is "null".
             // This should be considered a new "Product"
-            if (!$product || null !== $product->getId()) {
+            if (!$product || null === $product->getId()) {
                 $form->add('name', 'text');
             }
         });
@@ -212,7 +212,7 @@ class::
             $product = $event->getData();
             $form = $event->getForm();
 
-            if (!$product || null !== $product->getId()) {
+            if (!$product || null === $product->getId()) {
                 $form->add('name', 'text');
             }
         }