input: Write a function to print a staircase of height 'n' with '#' symbols, where each step is indented by spaces on the left. The staircase should be right-aligned. If the given height is an integer, then the function should print the staircase according to the height provided. If the height is not provided, return an empty string.
  assert staircase(5) == None
  assert staircase(3) == None
  assert staircase(0) == None
  assert staircase(-1) == None
  assert staircase(7) == None
output: def staircase(n=None):
      if n is None or n <= 0:
          return ""
      for i in range(1, n + 1):
          print(' ' * (n - i) + '#' * i)