input: Write a function to check if a given string contains the word "Hello". If it contains the word "Hello", return True, otherwise return False. If the string is empty or None, return False.
  assert check_hello("Hi, Hello there!")==True
  assert check_hello("Hi, there!")==False
  assert check_hello("Hello")==True
  assert check_hello("")==False
  assert check_hello(None)==False
output: def check_hello(s):
      if s is None or s == "":
          return False
      return "Hello" in s