Argument 1 must be pygame.Surface, not None how to decide?

Question

Python

Help solve the problem. Here is the error code: Traceback (most recent call last):
File "D:\Python\Pigs, escape from the farm\test.py", line 21, in
pygame.draw.rect(win, (0,0,255), ( x, y, width, height))
TypeError: argument 1 must be pygame.Surface, not None

import pygame

pygame.init()
win = pygame.display.set_mode((500, 500))
win = pygame.display.set_caption('Cubes Game')

x = 50
y = 50
width = 40
height = 60
speed = 5

run = True
while run:
  pygame.time.delay(100)

  for event in pygame.event.get():
    if event.type == pygame.QUIT:
      run = False

  pygame.draw.rect(win, (0,0,255), (x, y, width, height))
  pygame.display.update()

pygame.quit()