Fixed #4136 -- Made ModelForm save empty values for nullable CharFields as NULL.

Previously, empty values were saved as strings.

1 files changed, 5 insertions, 3 deletions

diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index a56c445c31..2435201db8 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -43,11 +43,13 @@ If ``True``, Django will store empty values as ``NULL`` in the database. Default
 is ``False``.
 
 Avoid using :attr:`~Field.null` on string-based fields such as
-:class:`CharField` and :class:`TextField` because empty string values will
-always be stored as empty strings, not as ``NULL``. If a string-based field has
+:class:`CharField` and :class:`TextField`. If a string-based field has
 ``null=True``, that means it has two possible values for "no data": ``NULL``,
 and the empty string. In most cases, it's redundant to have two possible values
-for "no data;" the Django convention is to use the empty string, not ``NULL``.
+for "no data;" the Django convention is to use the empty string, not
+``NULL``. One exception is when a :class:`CharField` has both ``unique=True``
+and ``blank=True`` set. In this situation, ``null=True`` is required to avoid
+unique constraint violations when saving multiple objects with blank values.
 
 For both string-based and non-string-based fields, you will also need to
 set ``blank=True`` if you wish to permit empty values in forms, as the