For the code below:
su = 0
def sod(N):
    global su
    su += N%10
        if N != 0:
            N = int(N/10)
            sod(N)
    return su
print(sod(int(input())))
The result is correct. For example., for input 16 its printing 7.
But for the code below
su = 0
def sod(N):
    global su
    su += N%10
        if N != 0:
            N = int(N/10)
            sod(N)
        else:
            return su
print(sod(int(input())))
The result is unexpected. Its printing None.
