How do you deal with empty rois

[twmht]

Hi,

Since FPN has a equation to map rois to different levels.

larger rois would be fed into deeper layers.

In the code (https://github.com/unsky/FPN/blob/master/lib/rpn/proposal_target_layer.py#L164), If there are no rois can be fed into the level (i.e., num_index==0), how do you deal with this issue?