bug fix for zero off-targets

tiger.py

@@ -340,11 +340,13 @@ def tiger_exhibit(transcripts: pd.DataFrame, mode: str, check_off_targets: bool,
     if check_off_targets and off_target_candidates is not None:
         off_target_candidates = find_off_targets(off_target_candidates, status_update_fn)
         off_target_predictions = predict_off_target(off_target_candidates, model=tiger)
-        off_target_predictions = off_target_predictions.sort_values(SCORE_COL, ascending=False).reset_index(drop=True)
+        if len(off_target_predictions) > 0:
+            off_target_predictions = off_target_predictions.sort_values(SCORE_COL, ascending=False)
+            off_target_predictions = off_target_predictions.reset_index(drop=True)
 
     # finalize tables
     for df in [on_target_predictions, titration_predictions, off_target_predictions]:
-        if df is not None:
+        if df is not None and len(df) > 0:
             df[GUIDE_COL] = df[GUIDE_COL].apply(lambda s: s[::-1])  # reverse guide sequences
             df[TARGET_COL] = df[TARGET_COL].apply(lambda seq: seq[CONTEXT_5P:len(seq) - CONTEXT_3P])  # remove context