Python: Unsupported operand while adding 2 functions output in python?

I am using python 3.8.8 and while running a simple program of Fibonacci it is giving me an error i.e. unsupported operand type(s) for +: 'NoneType' and 'NoneType'

def fibo(n):
if n <= 1:
    return("Hey! Please enter value greater than 1")
else:
    return((fibo(n-1)) + fibo(n-2))

nterms = 10
res = fibo(nterms)
print(res)

>Solution :

Add a return n to your code

def fib(n):
    if n<=1:
        return n 
    else:
        return(fib(n-1) + fib(n-2))

for i in range(10):
    print(f"fib({i}) = " + str(fib(i)))

gives

fib(0) = 0
fib(1) = 1
fib(2) = 1
fib(3) = 2
fib(4) = 3
fib(5) = 5
fib(6) = 8
fib(7) = 13
fib(8) = 21
fib(9) = 34