fix picodet postprocess for none-det case (#4462)

deploy/python/picodet_postprocess.py

@@ -193,13 +193,17 @@ class PicoDetPostProcess(object):
                     top_k=self.keep_top_k, )
                 picked_box_probs.append(box_probs)
                 picked_labels.extend([class_index] * box_probs.shape[0])
-            if not picked_box_probs:
-                return np.array([]), np.array([]), np.array([])
+
+            if len(picked_box_probs) == 0:
+                out_boxes_list.append(np.empty((0, 4)))
+                out_boxes_num.append(0)
+
+            else:
                 picked_box_probs = np.concatenate(picked_box_probs)
 
                 # resize output boxes
-            picked_box_probs[:, :4] = self.warp_boxes(picked_box_probs[:, :4],
-                                                      self.ori_shape[batch_id])
+                picked_box_probs[:, :4] = self.warp_boxes(
+                    picked_box_probs[:, :4], self.ori_shape[batch_id])
                 im_scale = np.concatenate([
                     self.scale_factor[batch_id][::-1],
                     self.scale_factor[batch_id][::-1]
@@ -210,7 +214,8 @@ class PicoDetPostProcess(object):
                     np.concatenate(
                         [
                             np.expand_dims(
-                            np.array(picked_labels), axis=-1), np.expand_dims(
+                                np.array(picked_labels),
+                                axis=-1), np.expand_dims(
                                     picked_box_probs[:, 4], axis=-1),
                             picked_box_probs[:, :4]
                         ],