How is top-k calculated?

[yangtle]

In the selection of queries between the encoder and decoder in the middle position, why are two classifiers set to None? The code is in deformable_transformer.py.
self.enc_out_class_embed = None
self.enc_out_bbox_embed = None
enc_outputs_class_unselected = self.enc_out_class_embed(output_memory)
enc_outputs_coord_unselected = self.enc_out_bbox_embed(output_memory) + output_proposals