bg image size is empty

[WillLiGitHub]

I change the max_char_length=30, then i get error:
dst = cv2.resize(dst, (dst_width, self.out_height), interpolation=cv2.INTER_CUBIC)
cv2.error: OpenCV(4.2.0) /io/opencv/modules/imgproc/src/resize.cpp:4045: error: (-215:Assertion failed) !ssize.empty() in function 'resize'

the problem is dst_bbox in dst = img[dst_bbox[1]:dst_bbox[1] + dst_bbox[3], dst_bbox[0]:dst_bbox[0] + dst_bbox[2]]

how can i fix?
best!