image_demo.py results in nan values in bboxes_pred

[AnaRhisT94]

Hi, Thanks for this amazing project @YunYang1994 .

When using the image_demo.py, I'm getting the following warnings:

/yolov3-tf2-master/YunYang1994_TF2_YoloV3/TensorFlow2.0-Examples/4-Object_Detection/YOLOV3/core/utils.py:221: RuntimeWarning: invalid value encountered in maximum
  pred_coor = np.concatenate([np.maximum(pred_coor[:, :2], [0, 0]),
/yolov3-tf2-master/YunYang1994_TF2_YoloV3/TensorFlow2.0-Examples/4-Object_Detection/YOLOV3/core/utils.py:222: RuntimeWarning: invalid value encountered in minimum
  np.minimum(pred_coor[:, 2:], [org_w - 1, org_h - 1])], axis=-1)
/yolov3-tf2-master/YunYang1994_TF2_YoloV3/TensorFlow2.0-Examples/4-Object_Detection/YOLOV3/core/utils.py:228: RuntimeWarning: invalid value encountered in greater
  scale_mask = np.logical_and((valid_scale[0] < bboxes_scale), (bboxes_scale < valid_scale[1]))
/yolov3-tf2-master/YunYang1994_TF2_YoloV3/TensorFlow2.0-Examples/4-Object_Detection/YOLOV3/core/utils.py:228: RuntimeWarning: invalid value encountered in less
  scale_mask = np.logical_and((valid_scale[0] < bboxes_scale), (bboxes_scale < valid_scale[1]))
/yolov3-tf2-master/YunYang1994_TF2_YoloV3

And afterwards, I'm printing the pred_bbox and bboxes. The predicted bboxes are almost all nans (and the value of bboxes doesn't matter because it uses pred_bbox):

tf.Tensor(
[[          nan           nan           nan ...           nan
            nan           nan]
 [          nan           nan           nan ...           nan
            nan           nan]
 [          nan           nan           nan ...           nan
            nan           nan]
 ...
 [3.8400000e+02 3.9251508e+02 2.5982959e+02 ... 1.7753243e-04
  5.0899386e-04 7.8248978e-04]
 [3.8401508e+02 3.8405893e+02 3.9810013e-02 ... 6.5720081e-04
  1.8835366e-03 2.6790202e-03]
 [3.8415375e+02 3.8413541e+02 7.9363394e-01 ... 1.9850866e-03
  2.3146670e-03 3.1724779e-03]], shape=(10647, 15), dtype=float32)

The output image has no bboxes. I'm using the weights that are downloaded from the link in your Readme file.