try fixing when model_type is None

app.py

@@ -95,6 +95,8 @@ def resize_fix_aspect_ratio(img, field, target_width=None, target_height=None):
 
 
 def inference(img, model_type):
+    if model_type is None:
+        return None, ""
     perspective_cfg_list = setup_cfg(model_zoo[model_type])
     demo = VisualizationDemo(cfg_list=perspective_cfg_list)
 
@@ -193,4 +195,4 @@ gr.Interface(
     description=description,
     article=article,
     examples=examples,
-).launch(share=True)
+).launch()