Empty training data was given. You'll need more than one sample to learn a model. in function 'cv::face::LBP

Question

I'm currently working on a face recognition project using Pycharm.

I used the following code for training:

import os
import cv2
from PIL import Image
import numpy as np
import pickle

BASE_DIR = os.path.dirname(os.path.abspath(__file__))
image_dir = os.path.join(BASE_DIR, "images")

face_cascade = cv2.CascadeClassifier('C:/Users/person/PycharmProjects/pythonProject/cascade/haarcascade_frontalface_default.xml')
recognizer = cv2.face.LBPHFaceRecognizer_create()
current_id = 0
label_ids = {}
y_labels = []
x_train = []

for root, dirs, files in os.walk(image_dir):
    for file in files:
        if file.endswith(".png") or file.endswith(".jpg"):
            path = os.path.join(root, file)
            label = os.path.basename(root).replace(" ", "-").lower()
           # print(label, path)
            if not label in label_ids:
                label_ids[label] = current_id
                current_id += 1

            id_ = label_ids[label]
           # print(label_ids)


            #y_labels.append(label)
            #x_train.append(path)

            pil_image = Image.open(path).conver("L")
            image_array = np.array(pil_image, "uint8")
            #print(image_array)

            faces = face_cascade.detectMultiScale(image_array, scaleFactor=1.5, minNeighbors=5)

            for (x, y, w, h) in faces:
                roi = image_array[y:y + h, x:x + w]
                x_train.append(roi)
                y_labels.append(id_)

#print(y_labels)
#print(x_train)

with open("labels.pickle", 'wb') as f:
    pickle.dump(label_ids, f)

recognizer.train(x_train, np.array(y_labels))
recognizer.save("C:/Users/person/PycharmProjects/pythonProject/recognizerstraining.yml")

Though I keep getting this error

Traceback (most recent call last):
  File "C:/Users/person/PycharmProjects/pythonProject/Train.py", line 51, in <module>
    recognizer.train(x_train, np.array(y_labels))
cv2.error: OpenCV(4.5.4-dev) D:\a\opencv-python\opencv-python\opencv_contrib\modules\face\src\lbph_faces.cpp:362: error: (-210:Unsupported format or combination of formats) Empty training data was given. You'll need more than one sample to learn a model. in function 'cv::face::LBPH::train

I've created a folder and inside this folder are multiple folders for each person. There are 7 images for each person.

So what might be the reason for the error?