--- og_aggregator.module	2009-11-16 22:52:49.000000000 +0100
+++ og_aggregator.module-hide-empty-block-patch	2009-11-16 22:49:43.000000000 +0100
@@ -192,7 +192,15 @@ l(t('more'), "node/$groupnode->nid/aggre
       while ($item = db_fetch_object($result)) {
         $items[] = theme('og_aggregator_block_item', $item);
       }
-      $block['content'] = theme('item_list', $items) . $block['content'];
+      # If the array $items is empty, return empty subject and content
+      # to hide the block instead of showing it empty
+      if (empty($items)) {
+        $block['subject'] = '';
+        $block['content'] = '';
+      } 
+      else {
+        $block['content'] = theme('item_list', $items) . $block['content'];
+      }
     }
     return $block;
   }