fix vlm return

app/business_logic.py

@@ -489,7 +489,7 @@ def vlm_auto_generate(image_target_state, image_reference_state, mask_target_sta
 
     if VLM_PROCESSOR is None or VLM_MODEL is None:
         gr.Warning("Please enable vlm for prompt first")
-        return prompt
+        return None
 
     messages = construct_vlm_gen_prompt(image_target_state, image_reference_state, mask_target_state, custmization_mode)
     output_text = run_vlm(VLM_PROCESSOR, VLM_MODEL, messages, device=device)