input: Write a function to find the largest number in the given list.
  assert find_largest_number([1000, 506, 299, 620, 35])==1000
  assert find_largest_number([34, 56, 78, 23, 45])==78
  assert find_largest_number([-1, -5, -3, -2])==-1
  assert find_largest_number([8])==8
  assert find_largest_number([])==None
output: def find_largest_number(numbers):
      if not numbers:
          return None
      return max(numbers)