Fix case with empty GT

Closes #309 (closed)

dan/ocr/manager/metrics.py

@@ -206,6 +206,8 @@ class MetricManager:
                     metrics["nb_" + keyword + suffix] = list(map(len, split_gt))
                     metrics[keyword + "_error_rate" + suffix] = [
                         round(float(edit_dist / gt_len), 4)
+                        if gt_len
+                        else float(bool(edit_dist))
                         for edit_dist, gt_len in zip(
                             metrics["edit_" + keyword + suffix],
                             metrics["nb_" + keyword + suffix],
                         )
                     ]
                 case "loss" | "loss_ce":
                     metrics[metric_name] = [
                         values[metric_name],