TypeError: cannot unpack non-iterable NoneType object Error

I looked at the other answers but they didn't seem to work for me, or I could just be doing something wrong, or not understanding what I am supposed to do in the context of this code. On line 78, it talks about how there is a Nonetype value, even though I assigned a value to both variables no matter what.

Here is a link to a similar problem (I think): [https://stackoverflow.com/questions/53680913/typeerror-cannot-unpack-non-iterable-nonetype-object][1]

Here is where I think the faulty code lies:

def check_win(turn, gamestate):
    if turn == 1:
        if gamestate[0] == gamestate[1] == gamestate[2] != '-' or gamestate[3] == gamestate[4] == gamestate[5] != '-' or gamestate[6] == gamestate[7] == gamestate[8] != '-':
            winner = 1
            win = True
            return winner, win
        elif gamestate[0] == gamestate[3] == gamestate[6] != '-' or gamestate[1] == gamestate[4] == gamestate[7] != '-' or gamestate[2] == gamestate[5] == gamestate[8] != '-':
            winner = 1
            win = True
            return winner, win
        elif gamestate[0] == gamestate[4] == gamestate[8] != '-' or gamestate[2] == gamestate[4] == gamestate[6] != '-':
            winner = 1
            win = True
            return winner, win
    elif turn == 2:
        if gamestate[0] == gamestate[1] == gamestate[2] or gamestate[3] == gamestate[4] == gamestate[5] or gamestate[6] == gamestate[7] == gamestate[8]:
            winner = 2
            win = True
            return winner, win
        elif gamestate[0] == gamestate[3] == gamestate[6] or gamestate[1] == gamestate[4] == gamestate[7] or gamestate[2] == gamestate[5] == gamestate[8]:
            winner = 2
            win = True
            return winner, win
        elif gamestate[0] == gamestate[4] == gamestate[8] or gamestate[2] == gamestate[4] == gamestate[6]:
            winner = 2
            win = True
            return winner, win
    else:
        winner = 'None' 
        win = False
        return winner, win

Later on when I try to alter those values in another function:

winner, win = check_win(turn, gamestate) <--- Where error was found

Here is the code in its entirety :

print('Tic Tac Toe:')
pos = 0
turn = 1
gamestate = ['-', '-', '-', '-', '-', '-', '-', '-', '-']

def display_board(gamestate):
    print(gamestate[0:3])
    print(gamestate[3:6])
    print(gamestate[6:9])
def move_validity(pos, gamestate):
    if str(gamestate[int(pos)]) != '-':
        print('Invalid move.')
        valid = False
        return valid
    else:
        valid = True
        return valid
def update(gamestate, pos):
        if turn == 1:
            gamestate[int(pos)] = 'X'
        if turn == 2:
            gamestate[int(pos)] = 'O'
        else:
            print('ERROR')
def check_win(turn, gamestate):
    if turn == 1:
        if gamestate[0] == gamestate[1] == gamestate[2] != '-' or gamestate[3] == gamestate[4] == gamestate[5] != '-' or gamestate[6] == gamestate[7] == gamestate[8] != '-':
            winner = 1
            win = True
            return winner, win
        elif gamestate[0] == gamestate[3] == gamestate[6] != '-' or gamestate[1] == gamestate[4] == gamestate[7] != '-' or gamestate[2] == gamestate[5] == gamestate[8] != '-':
            winner = 1
            win = True
            return winner, win
        elif gamestate[0] == gamestate[4] == gamestate[8] != '-' or gamestate[2] == gamestate[4] == gamestate[6] != '-':
            winner = 1
            win = True
            return winner, win
    elif turn == 2:
        if gamestate[0] == gamestate[1] == gamestate[2] or gamestate[3] == gamestate[4] == gamestate[5] or gamestate[6] == gamestate[7] == gamestate[8]:
            winner = 2
            win = True
            return winner, win
        elif gamestate[0] == gamestate[3] == gamestate[6] or gamestate[1] == gamestate[4] == gamestate[7] or gamestate[2] == gamestate[5] == gamestate[8]:
            winner = 2
            win = True
            return winner, win
        elif gamestate[0] == gamestate[4] == gamestate[8] or gamestate[2] == gamestate[4] == gamestate[6]:
            winner = 2
            win = True
            return winner, win
    else:
        winner = 'None'
        win = False
        return winner, win
def restart():
    gamestate = ['-', '-', '-', '-', '-', '-', '-', '-', '-']
    turn = 1
    win = False
    return gamestate, turn, win
def choose_position():
    pos = input('Player ' + str(turn) + ': ')
    if int(pos) < 0 or int(pos) > 8:
        print('Invalid move')
    else:
        return pos
def Tic_Tac_Toe():
    while True:
        global pos
        global turn
        if turn == 1:
            pos = choose_position()
            valid = move_validity(pos, gamestate)
            if valid == True:
                update(gamestate, pos)
            if valid == False:
                break
            winner, win = check_win(turn, gamestate)
            if win == True:
                print(str(winner) + ' wins!')
                break
            if '-' not in gamestate:
                print('Tie game.')
                break
        if turn == 2:
            pos = choose_position()
            if move_validity(pos, gamestate) == True:
                continue
            if move_validity(pos, gamestate) == False:
                break
            update(gamestate, pos)
            winner, win = check_win(turn, gamestate)
            if win == True:
                print(str(winner) + ' wins!')
                break
            turn = 1
            if '-' not in gamestate:
                print('Tie game.')
                break

        display_board(gamestate)
display_board(gamestate)
Tic_Tac_Toe()
restart_case = input('y/n Would you like to play? ')
if restart_case == 'y':
    gameboard, turn, win = restart()

Thank you so much, and sorry if the solution was a small typo, I am really new to this and have spent way too much time on this. :D