input: Write a python function to handle division by zero and print an error message.
  assert safe_divide(10, 0) is None
  assert safe_divide(10, 2) == 5
  assert safe_divide(5, 1) == 5
output: def safe_divide(a, b):
      try:
          return a / b
      except ZeroDivisionError:
          print("Error: Division by zero is not allowed.")
          return None