docs: update docs

Author: kenjis

user_guide_src/source/changelogs/v4.3.4.rst

@@ -35,6 +35,19 @@ Redirect Status Code
   always be used when you don't specify a status code. In previous versions,
   302 might be changed.
 
+Forge::modifyColumn()
+---------------------
+
+- The :ref:`$forge->modifyColumn() <db-forge-modifyColumn>` has been fixed. Due
+  to a bug, in previous versions, SQLite3/Postgres/SQLSRV might change
+  ``NULL``/``NOT NULL`` unpredictably.
+- In previous versions, the OCI8 driver did not change ``NULL``/``NOT NULL``
+  when you don't specify ``null`` value.
+- Now in all database drivers ``$forge->modifyColumn()`` always sets ``NULL``
+  when you don't specify ``null`` value.
+- The ``NULL``/``NOT NULL`` change may still be unexpectedly, it is recommended
+  to always specifiy ``null`` value.
+
 Message Changes
 ***************
 

user_guide_src/source/dbmgmt/forge.rst

@@ -285,6 +285,8 @@ Used to remove multiple columns from a table.
 Modifying a Field in a Table
 ============================
 
+.. _db-forge-modifyColumn:
+
 $forge->modifyColumn()
 ----------------------
 
@@ -295,7 +297,9 @@ change the name, you can add a "name" key into the field defining array.
 .. literalinclude:: forge/026.php
 
 .. note:: The ``modifyColumn()`` may unexpectedly change ``NULL``/``NOT NULL``.
-    So it is recommended to always specify ``null`` value.
+    So it is recommended to always specify ``null`` value. Unlike when creating
+    a table, if ``null`` is not specified, the column will be ``NULL``, not
+    ``NOT NULL``.
 
 .. note:: Due to a bug, prior v4.3.3, SQLite3 may not set ``NOT NULL`` even if you
     specify ``'null' => false``.