add None option for speaker

app.py

@@ -144,7 +144,7 @@ def predict(audio, src_language, tgt_language, mic_audio=None):
             'prev_output_tokens': None,
         },
         'target_lengths': None,
-        'speaker': tts_sample['speaker'].to(device)
+        'speaker': tts_sample['speaker'].to(device) if tts_sample['speaker'] is not None else None,
     }    
 
     wav, rate = TTSHubInterface.get_prediction(tts_task, tts_model, tts_generator, tts_sample)