fix webchat

src/llamafactory/webui/chatter.py

@@ -144,8 +144,8 @@ class WebChatModel(ChatModel):
             messages,
             system,
             tools,
-            images=[image],
-            videos=[video],
+            images=[image] if image else None,
+            videos=[video] if video else None,
             max_new_tokens=max_new_tokens,
             top_p=top_p,
             temperature=temperature,