Update app.py

app.py

@@ -84,7 +84,7 @@ def generate(prompt, quality_tags, neg_prompt, seed, scale, width, height, steps
         smea, dyn, dyn_threshold, cfg_rescale
     )
     if not isinstance(img_data, bytes):
-        return -1, payload
+        return None, payload
     today_count += 1
     img = image_from_bytes(img_data)