fix default offset not set when running array_filter

example.php

@@ -86,7 +86,7 @@ $client->api('issue')->all(array(
 ));
 $client->api('issue')->all(array('category_id'    => $categoryId));
 $client->api('issue')->all(array('tracker_id'     => $trackerId));
-$client->api('issue')->all(array('tracker_id'     => 'closed'));
+$client->api('issue')->all(array('status_id'      => 'closed'));
 $client->api('issue')->all(array('assigned_to_id' => $userId));
 $client->api('issue')->all(array('project_id'     => 'test'));
 $client->api('issue')->all(array(

lib/Redmine/Api/AbstractApi.php

@@ -88,10 +88,13 @@ abstract class AbstractApi
             'limit'  => 25,
             'offset' => 0,
         );
-        $params = array_filter(array_merge($defaults, $params));
+        $params = array_filter(
+            array_merge($defaults, $params),
+            array($this, 'isNotNull')
+        );
 
         $ret = array();
-        
+
         $limit = $params['limit'];
         $offset = $params['offset'];