fix: model revision handling

app.py

@@ -93,8 +93,8 @@ def process_refexp(image: Image, prompt: str, model_revision: str = 'main'):
 
     print(f"(image, prompt): {image}, {prompt}")
 
-    if not pretrained_revision:
-        pretrained_revision = 'main'
+    if not model_revision:
+        model_revision = 'main'
     
     print(f"model checkpoint revision: {model_revision}")