binary segmentation，mcc for category is nan

[idazhuang]

I want to do edge segmentation of rocks，but got this error.
before this，I did the region segmentation of rocks in the same rock picture. Didn’t get this error.

I used the following method to transform json to label.

ensure_dir(INPUT_DIR)

# ensure_dir(OUTPUT_DIR)
category_types = ["background", "chips"]
# empty_dir(OUTPUT_DIR)
# empty_dir(label_DIR)
# empty_dir(side_DIR)
""" Browse through all marked json files """
for file in iglob(INPUT_DIR + '/*.json'):
    with open(file, 'r', encoding='utf-8') as f:

        """ Load json files """
        data = json.load(f)

        """ Save image file """
        j_name = file.split("\\")[-1]
        ts = j_name.split(".")
        title = ts[0]
        file_name = join(img_DIR, "%s.jpg"%title)
        print(file_name, file)
        img_ori = cv2.imread(file_name, cv2.IMREAD_GRAYSCALE)  #3通道变灰度图单通道
        #cv2.imshow('a',img_ori)
        size_ori = img_ori.shape
        #print(size_ori)
        """ Get image width x height """
        mask = np.zeros((size_ori[0], size_ori[1]), dtype="uint8") #全黑图
        sideImg = np.zeros((size_ori[0], size_ori[1]), dtype="uint8")

        """ Process each shape (annotation) """
        for shape in data['shapes']:
            category = shape["label"]
            points = shape["points"]
            # 填充
            points_array = np.array(points, dtype=np.int32)
            mask = cv2.fillPoly(mask, [points_array], (255, 255, 255), category_types.index(category))
            sideImg = cv2.drawContours(sideImg, [points_array], -1, (255, 255, 255), 3, category_types.index(category))



        # cv2.imshow("mak:", mask)
        # cv2.polylines
        save_name = join(label_DIR, title) + ".png"
        cv2.imwrite(save_name, mask)
        save_name = join(side_DIR, title) + ".png"
        cv2.imwrite(save_name, sideImg)

Anyone met the same error?