运行这行代码时，我收到此错误：
img = cv2.resize(img, (224,224))
OpenCV(4.1.2) C:\projects\opencv-python\opencv\modules\imgproc\src\resize.cpp:3720: error: (-215:Assertion failed) !ssize.empty() in function 'cv::调整大小'
python opencv computer-vision cv2
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