fix empty input catch

app.py

@@ -10,8 +10,8 @@ You are given a short description of a person. Respond only with three different
 """
 
 def get_vibe(caption):
-    if caption is None:
-        return "No caption provided."
+    if not caption or not caption.strip():
+        raise gr.Error("No caption provided.")
 
     messages = [
         {"role": "system", "content": system_instruction},