Fix bug cuando listado es vacío

Admin/WorkflowBaseAdmin.php

@@ -16,7 +16,8 @@ class WorkflowBaseAdmin extends BaseAdmin
 
         $workflows = $this->getRepository('WorkflowBundle:Workflow')->findAllByClass($this->getClass());
         foreach ($workflows as $workflow) {
-            $transitions = $workflow->getDefinition($workflow->getSubject())->getTransitions();
+            $definition = $workflow->getDefinition($workflow->getSubject());
+            $transitions = $definition ? $definition->getTransitions() : array();
             foreach ($transitions as $key => $transition) {
                 $actions[$key] = array(
                     'label' => $this->trans('workflow.' . $workflow->getName() . '.transitions.' . $transition->getName(), array(), 'WorkflowLabel'),