Make sure $caller has a name (#13)

Author: Nyholm

src/Visitor/Php/Symfony/FlashMessage.php

@@ -31,7 +31,8 @@ public function enterNode(Node $node)
 
             $name = $node->name;
             $caller = $node->var;
-            $callerName = $caller->name;
+            // $caller might be "Node\Expr\New_"
+            $callerName = isset($caller->name) ? $caller->name : '';
 
             /*
              * Make sure the caller is from a variable named "this" or a function called "getFlashbag"