diff --git a/src/Messages/SendMessageCommand.php b/src/Messages/SendMessageCommand.php
index b62ed21..2cb7b2a 100644
--- a/src/Messages/SendMessageCommand.php
+++ b/src/Messages/SendMessageCommand.php
@@ -19,7 +19,7 @@ class SendMessageCommand
      * @param Model        $sender       The sender identifier
      * @param string       $type         The message type
      */
-    public function __construct(Conversation $conversation, $body, Model $sender, $type = 'text', $data)
+    public function __construct(Conversation $conversation, $body, Model $sender, $type = 'text', $data = null)
     {
         $this->conversation = $conversation;
         $this->body = $body;