Add "Casting to NULL" section back, this time with correct content.

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@322850 c90b9560-bf6c-de11-be94-00142212c4b1

language/types/null.xml

@@ -54,6 +54,17 @@ $var = NULL;
   </para>
 
  </sect2>
+ 
+ <sect2 xml:id="language.types.null.casting">
+  <title>Casting to <literal>NULL</literal></title>
+
+  <para>
+   Casting a variable to <type>null</type> using <literal>(unset) $var</literal>
+   will <emphasis>not</emphasis> remove the variable or unset its value.
+   It will only return a &null; value.
+  </para>
+
+ </sect2>
 
 </sect1>