Why does keras-yolov3 data generator return target as zeros

[Sid Anand]

Why does the data generator return zeros for the target (https://github.com/qqwweee/keras-yolo3/blob/master/train.py#L182)

All the image,bounding boxes and label data is fed into the inputs while the targets are zeros

Why is this done? It is my understanding that the inputs should have the image data while the targets should have the bounding boxes data and the labels