postgresql - error on pkg installation

#### Steps to reproduce the issue
try to install on postgresql


#### Expected result
it install


#### Actual result
don't install 


#### System information (as much as possible)
Weblinks 3.4.1 Release Candidate 2
PostgreSQL 9.3.5
Joomla 3.4.4-dev

#### Additional comments
without the setting give an invalid timestamp for the category table

src/com_weblinks/script.php

@@ -42,6 +42,7 @@ class Com_WeblinksInstallerScript
 			$category->params = '{"category_layout":"","image":""}';
 			$category->metadata = '{"author":"","robots":""}';
 			$category->language = '*';
+			$category->checked_out_time = JFactory::getDbo()->quote(JFactory::getDbo()->getNullDate());
 
 			// Set the location in the tree
 			$category->setLocation(1, 'last-child');