Updated the example add added a caution

Author: HeahDude

reference/forms/types/options/empty_data.rst.inc

@@ -10,35 +10,31 @@ empty_data
 DEFAULT_PLACEHOLDER
 
 This option determines what value the field will return when the submitted
-value is empty. It does not set an initial value if none is provided when
-the form is rendered in a view (see ``data`` or ``placeholder`` options).
+value is empty (or missing). It does not set an initial value if none is
+provided when the form is rendered in a view (see ``data`` or ``placeholder``
+options).
 
 It helps you handling form submission and you can customize this to your needs.
-For example, if you want the ``gender`` choice field to be explicitly set to ``Male``
+For example, if you want the ``name`` field to be explicitly set to ``John Doe``
 when no value is selected, you can do it like this::
 
-    $builder->add('gender', 'choice', array(
-        'choices' => array(
-            'm' => 'Male',
-            'f' => 'Female',
-        ),
+    $builder->add('name', null, array(
         'required'    => false,
-        'empty_value' => 'Choose your gender',
-        'empty_data'  => 'm',
+        'empty_data'  => 'John Doe',
     ));
 
-If a form is compound, you can set ``empty_data`` as an array with fields names
+If a form is compound, you can set ``empty_data`` as an array with field names
 as keys and submitted values as string values (or arrays if nested fields are
 also compound).
 
-.. caution::
-
-    In this example, the choice field is not set as ``multiple``. If it was
-    ``empty_data`` option should be an array of submitted string values::
-
-        'empty_data' => array('m'),
-
 .. note::
 
     If you want to set the ``empty_data`` option for your entire form class,
     see the cookbook article :doc:`/cookbook/form/use_empty_data`.
+
+.. caution::
+
+    When using `empty_data` as an empty string, the form will always return
+    ``null``. If you need to get an empty string to be returned, you should
+    use a data transformer, see the cookbook article
+    :doc:`cookbook/form/data_transformers`.