input: Write a function to identify the largest number in the given list. If the list is empty, return None.
  assert find_max_number([1000, 506, 299, 620, 35]) == 1000
  assert find_max_number([-10, -20, -30, -5]) == -5
  assert find_max_number([5]) == 5
  assert find_max_number([]) == None
  assert find_max_number([45, 45, 45]) == 45
output: def find_max_number(numbers):
      if not numbers:
          return None
      return max(numbers)