fixup

Author: HeahDude

reference/forms/types/choice.rst

@@ -122,7 +122,13 @@ method::
     ]);
 
 You can also customize the `choice_name`_ of each choice. You can learn more
-about all of them in the sections below.
+about all of these options in the sections below.
+
+.. caution::
+
+    The *placeholder* is a specific field, when the choices are optional the
+    first item in the list must be empty, so the user can unselect.
+    Be sure to always handle the empty choice ``null`` when using callbacks.
 
 .. _forms-reference-choice-tags: