diff --git a/src/admin/common/abstract/model.php b/src/admin/common/abstract/model.php
index 9a1561f..41829ef 100644
--- a/src/admin/common/abstract/model.php
+++ b/src/admin/common/abstract/model.php
@@ -117,6 +117,9 @@ abstract class AbstractCommonClubsModel
             if($v['type'] !== 'ref')
                 continue;
             
+            if(is_null($vals[$k]))
+                continue;
+            
             $vals[$k] = $vals[$k]->getId();
         }
         
@@ -133,6 +136,9 @@ abstract class AbstractCommonClubsModel
             if(empty($v['ref']))
                 throw new Exception('External reference of unknown class found.');
             
+            if(empty($vals[$k]))
+                continue;
+            
             $vals[$k] = $this->loadExternalReferenceAsObject($v['ref'], $vals[$k]);
         }
         
@@ -304,6 +310,7 @@ abstract class AbstractCommonClubsModel
         $q->where("id = {$this->id}");
     }
     
+    // FIXME Add additional filter to remove associations of the object
     public function delete()
     {
         $db = Factory::getDbo();
diff --git a/src/admin/common/abstract/model/factory.php b/src/admin/common/abstract/model/factory.php
index 491799c..bb60ee9 100644
--- a/src/admin/common/abstract/model/factory.php
+++ b/src/admin/common/abstract/model/factory.php
@@ -30,6 +30,7 @@ abstract class AbstractCommonClubsModelFactory
      *      - int
      *      - float
      *      - ref
+     *  - optional: boolean, if true, the field can be NULL
      *  - ref: (only with type='ref') The name of the class that is referenced
      */
     public abstract function getAttributes();
diff --git a/src/admin/common/models/factory/place.php b/src/admin/common/models/factory/place.php
index a08046e..c8f1bd8 100644
--- a/src/admin/common/models/factory/place.php
+++ b/src/admin/common/models/factory/place.php
@@ -9,7 +9,8 @@ class CommonClubsModelFactoryPlace extends AbstractCommonClubsModelFactory
     {
         return array(
             'name'=>array(),
-            'club'=>array('col'=>'clubid', 'type'=>'ref', 'ref'=>'CommonClubsModelClub')
+            'club'=>array('col'=>'clubid', 'type'=>'ref', 'ref'=>'CommonClubsModelClub'),
+            'area'=>array('type'=>'int', 'optional'=>true)
         );
     }