Update app.py

app.py

@@ -135,7 +135,7 @@ def run_voice_clone_tts(
         inputs = processor(
             text=text.lower(),
             prompt_speech_path=prompt_speech_path,
-            prompt_text=prompt_text_clean.lower(),
+            prompt_text=prompt_text_clean.lower() if prompt_text_clean else prompt_text_clean,
             return_tensors="pt"
         ).to(device) # Move processor output to model device