[PY-611] Silently ignore "empty" masks during import (#741)

* update darwin import - removing masks that do not have a corresponding raster layer

* update importer - optimize code by using `sets`

darwin/importer/importer.py

@@ -743,6 +743,8 @@ def _import_annotations(
     errors: dt.ErrorList = []
     success: dt.Success = dt.Success.SUCCESS
 
+    rl: Optional[dt.Annotation] = None
+    rl_dense_rle_ids: Optional[Set[str]] = None
     serialized_annotations = []
     for annotation in annotations:
         annotation_class = annotation.annotation_class
@@ -771,6 +773,33 @@ def _import_annotations(
 
         data = _get_annotation_data(annotation, annotation_class_id, attributes)
 
+        # check if the mask is empty (i.e. masks that do not have a corresponding raster layer) if so, skip import of the mask
+        if annotation_type == "mask":
+            if rl is None:
+                rl = next(
+                    (
+                        a
+                        for a in annotations
+                        if a.annotation_class.annotation_type == "raster_layer"
+                    ),
+                    None,
+                )
+            if rl and rl_dense_rle_ids is None:
+                rl_dense_rle_ids = set(rl.data["dense_rle"][::2])
+            if rl is not None and rl_dense_rle_ids is not None:
+                # check if the 'annotation_class_id' is in raster_layer's mask_annotation_ids_mapping dict
+                _annotation_id = annotation.id
+                if (
+                    rl.data["mask_annotation_ids_mapping"][_annotation_id]
+                    not in rl_dense_rle_ids
+                ):
+                    # skip import of the mask, and remove it from mask_annotation_ids_mapping
+                    logger.warning(
+                        f"Skipping import of mask annotation '{annotation_class.name}' as it does not have a corresponding raster layer"
+                    )
+                    del rl.data["mask_annotation_ids_mapping"][_annotation_id]
+                    continue
+
         actors: List[dt.DictFreeForm] = []
         actors.extend(_handle_annotators(annotation, import_annotators))
         actors.extend(_handle_reviewers(annotation, import_reviewers))