Update ui.py

ui.py

@@ -146,7 +146,8 @@ def save_row(idx: int, ratings: List[str], comments: List[str]):
         df.at[idx, f"rating_{m}__prompt2"] = ratings[p]; p += 1
     # comments
     for m, c in zip(order, comments):
-        df.at[idx, f"{COMMENT_PREFIX}{m}"] = c.strip() or "no comment"
+        clean = (c or "").strip()
+        df.at[idx, f"{COMMENT_PREFIX}{m}"] = clean or "no comment"
 
     df.at[idx, "annotator"]       = annotator
     df.at[idx, "annotation_time"] = float(elapsed)