get staff with null api_token

app/Http/Controllers/Controller.php

@@ -120,7 +120,7 @@ class Controller extends BaseController
 
     public function getDatabase(Request $request)
     {
-        $staff = Staff::where('api_token', '')->where('roles_access', 'Installer')->get();
+        $staff = Staff::where('api_token', null)->where('roles_access', 'Installer')->get();
     
         return $staff;
     }