fix: handle empty string for model revision

app.py

@@ -92,6 +92,10 @@ def translate_point_coords_from_out_to_in(point=None, input_image_size=None, out
 def process_refexp(image: Image, prompt: str, model_revision: str = 'main'):
 
     print(f"(image, prompt): {image}, {prompt}")
+
+    if not pretrained_revision:
+        pretrained_revision = 'main'
+    
     print(f"model checkpoint revision: {model_revision}")
 
     load_model(model_revision)