Handle empty image input

app.py

@@ -43,6 +43,8 @@ class App:
         return model
 
     def __call__(self, model_name, image):
+        if image is None:
+            return ''
         model = self._get_model(model_name)
         image = self._preprocess(image.convert('RGB')).unsqueeze(0)
         # Greedy decoding