Fix issue spotted while testing

inference/core/workflows/core_steps/common/query_language/operations/detections/base.py

@@ -384,7 +384,7 @@ def _pick_detections_by_parent_class(
     parent_class: str,
 ) -> sv.Detections:
     class_names = detections.data.get("class_name")
-    if not class_names:
+    if class_names is None or len(class_names) == 0:
         return sv.Detections.empty()
     if not isinstance(class_names, np.ndarray):
         class_names = np.array(class_names)

tests/workflows/unit_tests/core_steps/common/query_language/operations/test_detections_operations.py

@@ -143,7 +143,7 @@ def test_picking_detections_by_parent_class_when_parent_class_not_fond() -> None
         ),
         class_id=np.array([0, 1]),
         confidence=np.array([0.3, 0.4]),
-        data={"class_name": ["c", "d"]},
+        data={"class_name": np.array(["c", "d"])},
     )
 
     # when
@@ -166,7 +166,7 @@ def test_picking_detections_by_parent_class_when_no_child_detections_matching()
         ),
         class_id=np.array([0, 0, 1]),
         confidence=np.array([0.3, 0.4, 0.5]),
-        data={"class_name": ["a", "a", "b"]},
+        data={"class_name": np.array(["a", "a", "b"])},
     )
 
     # when
@@ -191,7 +191,7 @@ def test_picking_detections_by_parent_class_when_there_are_child_detections_matc
         ),
         class_id=np.array([0, 1, 1]),
         confidence=np.array([0.3, 0.4, 0.5]),
-        data={"class_name": ["a", "b", "b"]},
+        data={"class_name": np.array(["a", "b", "b"])},
     )
 
     # when
@@ -220,7 +220,7 @@ def test_picking_detections_by_parent_class_when_there_are_child_detections_matc
         ),
         class_id=np.array([0, 1, 1, 0, 2]),
         confidence=np.array([0.3, 0.4, 0.5, 0.6, 0.7]),
-        data={"class_name": ["a", "b", "b", "a", "c"]},
+        data={"class_name": np.array(["a", "b", "b", "a", "c"])},
     )
 
     # when