config_item() to return NULL instead of FALSE for non-existing items

Close #3001
Close #3232
Related: #3244
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index a3b3549..0e49302 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -492,6 +492,7 @@
       -  Changed internal function ``load_class()`` to accept a constructor parameter instead of (previously unused) class name prefix.
       -  Removed default parameter value of :func:`is_php()`.
       -  Added a second argument ``$double_encode`` to :func:`html_escape()`.
+      -  Changed function ``config_item()`` to return NULL instead of FALSE when no value is found.
 
    -  :doc:`Output Library <libraries/output>` changes include:
 
diff --git a/user_guide_src/source/general/common_functions.rst b/user_guide_src/source/general/common_functions.rst
index 9c0a7cb..399a323 100644
--- a/user_guide_src/source/general/common_functions.rst
+++ b/user_guide_src/source/general/common_functions.rst
@@ -63,7 +63,7 @@
 .. function:: config_item($key)
 
 	:param	string	$key: Config item key
-	:returns:	Configuration key value or FALSE if not found
+	:returns:	Configuration key value or NULL if not found
 	:rtype:	mixed
 
 	The :doc:`Config Library <../libraries/config>` is the preferred way of
diff --git a/user_guide_src/source/installation/upgrade_300.rst b/user_guide_src/source/installation/upgrade_300.rst
index 6915faf..81340e6 100644
--- a/user_guide_src/source/installation/upgrade_300.rst
+++ b/user_guide_src/source/installation/upgrade_300.rst
@@ -158,6 +158,10 @@
 
 Many methods and functions now return NULL instead of FALSE when the required items don't exist:
 
+ - :doc:`Common functions <../general/common_functions>`
+
+   - config_item()
+
  - :doc:`Config Class <../libraries/config>`
 
    - config->item()