Fix incorrect placement of is_empty_callback

Author: janklan

reference/forms/types/form.rst

@@ -61,16 +61,17 @@ The actual default value of this option depends on other field options:
 * If ``data_class`` is not set and ``compound`` is ``false``, then ``''``
   (empty string).
 
+.. include:: /reference/forms/types/options/empty_data_description.rst.inc
+
+.. _reference-form-option-error-bubbling:
+
 ``is_empty_callback``
 ~~~~~~~~~~~~~~~~~~~~~
 
 **type**: ``callable`` **default**: ``null``
 
 This callable takes form data and returns whether value is considered empty.
 
-.. include:: /reference/forms/types/options/empty_data_description.rst.inc
-
-.. _reference-form-option-error-bubbling:
 
 .. include:: /reference/forms/types/options/error_bubbling.rst.inc