System information (version)

• OpenCV => 3.4
• Operating System / Platform => Ubuntu 18.

Detailed description

Problem : Loading any model from ONNX model zoo / Image Manipulation / Fast Neural style transfer for example , Candy model (direct link) gives error -

cv2.error: OpenCV(4.2.0-dev) /home/usr/opencv/modules/dnn/src/dnn.cpp:4600: error: (-215:Assertion failed) inputs.size() in function 'getMemoryShapes'

Steps to reproduce

import cv2
net = cv2.dnn.readNetFromONNX("/Path_to_model/candy.onnx")