IndexError: list index out of rangeを解決したい

$ display_image_samples(dataset_train)
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-27-d2d5c6187cf9> in <module>()
----> 1 display_image_samples(dataset_train)

1 frames
/content/Mask_RCNN/mrcnn/visualize.py in display_top_masks(image, mask, class_ids, class_names, limit)
    321     #    m = np.sum(m * np.arange(1, m.shape[-1] + 1), -1)
    322     #    to_display.append(m)
--> 323     #    titles.append(class_names[class_id] if class_id != -1 else "-")
    324     display_images(to_display, titles=titles, cols=limit + 1, cmap="Blues_r")
    325 

IndexError: list index out of range

def display_top_masks(image, mask, class_ids, class_names, limit=4):
    """Display the given image and the top few class masks."""
    to_display = []
    titles = []
    to_display.append(image)
    titles.append("H x W={}x{}".format(image.shape[0], image.shape[1]))
    # Pick top prominent classes in this image
    unique_class_ids = np.unique(class_ids)
    mask_area = [np.sum(mask[:, :, np.where(class_ids == i)[0]])
                 for i in unique_class_ids]
    top_ids = [v[0] for v in sorted(zip(unique_class_ids, mask_area),
                                    key=lambda r: r[1], reverse=True) if v[1] > 0]
    Generate images and titles
    for i in range(limit):
       class_id = top_ids[i] if i < len(top_ids) else -1
        # Pull masks of instances belonging to the same class.
        m = mask[:, :, np.where(class_ids == class_id)[0]]
        m = np.sum(m * np.arange(1, m.shape[-1] + 1), -1)
        to_display.append(m)
        titles.append(class_names[class_id] if class_id != -1 else "-")
    display_images(to_display, titles=titles, cols=limit + 1, cmap="Blues_r")