The Collatz Sequence

[Truman]

Write a function named collatz() that has one parameter named number. If number is even, then collatz() should print number // 2 and return this value. If number is odd, then collatz() should print and return 3 * number + 1.
Then write a program that lets the user type in an integer and that keeps calling collatz() on that number until the function returns the value 1.

def collatz(number):
    if number % 2 == 0:
        print(number//2)
    else:    
        result = 3*number + 1
        print(result)        
try:
    n = input("Give me a number: ")
    while n != 1:
        n = collatz(int(n))
except ValueError:
    print('Type a number please!')

message:
Traceback (most recent call last):
File "C:\Python36\kodovi\coll.py", line 10, in <module>
n = collatz(int(n))
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'

Not sure why am I receiving this message.