Merge branch '4.4' into 5.2

* 4.4:
  [Validator] Mention IsNull in Basic Constraints
  Show example how to set xdebug.file_link_format

Author: javiereguiluz

reference/configuration/framework.rst

@@ -462,7 +462,13 @@ Since every developer uses a different IDE, the recommended way to enable this
 feature is to configure it on a system level. This can be done by setting the
 ``xdebug.file_link_format`` option in your ``php.ini`` configuration file. The
 format to use is the same as for the ``framework.ide`` option, but without the
-need to escape the percent signs (``%``) by doubling them.
+need to escape the percent signs (``%``) by doubling them::
+
+    // example for PhpStorm
+    xdebug.file_link_format="phpstorm://open?file=%f&line=%l"
+
+    // example for Sublime
+    xdebug.file_link_format="subl://open?url=file://%f&line=%l"
 
 .. note::
 

reference/constraints/IsFalse.rst

@@ -125,6 +125,8 @@ method returns **false**:
             // ...
         }
 
+.. include:: /reference/constraints/_null-values-are-valid.rst.inc
+
 Options
 -------
 

reference/constraints/IsTrue.rst

@@ -129,6 +129,8 @@ Then you can validate this method with ``IsTrue`` as follows:
 
 If the ``isTokenValid()`` returns false, the validation will fail.
 
+.. include:: /reference/constraints/_null-values-are-valid.rst.inc
+
 Options
 -------
 

reference/constraints/Type.rst

@@ -169,6 +169,8 @@ This will check if ``emailAddress`` is an instance of ``Symfony\Component\Mime\A
             }
         }
 
+.. include:: /reference/constraints/_null-values-are-valid.rst.inc
+
 Options
 -------
 

reference/constraints/_null-values-are-valid.rst.inc

@@ -0,0 +1,6 @@
+.. note::
+
+    As with most of the other constraints, ``null`` is
+    considered a valid value. This is to allow the use of optional values.
+    If the value is mandatory, a common solution is to combine this constraint
+    with :doc:`NotNull </reference/constraints/NotNull>`.