Add default value to setFetchMode's $constructorArgs with FETCH_CLASS

Closes GH-1436.

Author: Seldaek

reference/pdo/pdostatement/setfetchmode.xml

@@ -25,7 +25,7 @@
    <modifier>public</modifier> <type>bool</type><methodname>PDOStatement::setFetchMode</methodname>
    <methodparam><type>int</type><parameter>mode</parameter><initializer>PDO::FETCH_CLASS</initializer></methodparam>
    <methodparam><type>string</type><parameter>class</parameter></methodparam>
-   <methodparam><type class="union"><type>array</type><type>null</type></type><parameter>constructorArgs</parameter></methodparam>
+   <methodparam><type class="union"><type>array</type><type>null</type></type><parameter>constructorArgs</parameter><initializer>&null;</initializer></methodparam>
   </methodsynopsis>
 
   <methodsynopsis>