Tweak print logic

drivers/command_driver.py

@@ -32,7 +32,8 @@ class TerminalBot(rollbot.Rollbot[str]):
         )
 
     async def respond(self, res):
-        print(res.text, flush=True)
+        if res.text is not None:
+            print(res.text, flush=True)
         for att in res.attachments:
             print(f"Attached: {att.name}", flush=True)