diff --git a/application/controllers/api/v1/Categories.php b/application/controllers/api/v1/Categories.php
index 3e1c8b86..6e9d3aca 100644
--- a/application/controllers/api/v1/Categories.php
+++ b/application/controllers/api/v1/Categories.php
@@ -71,7 +71,7 @@ class Categories extends API_V1_Controller {
     {
         try
         {
-            $condition = $id !== NULL ? 'id = ' . $id : '';
+            $condition = $id !== NULL ? 'id = ' . $id : NULL;
             $categories = $this->services_model->get_all_categories($condition);
 
             if ($id !== NULL && count($categories) === 0)