input: Write a function to format a two-dimensional array as a table. If the given array is empty then return None.
  assert printTable([[1, 2, 3], [4, 5, 6], [7, 8, 9]])==None
  assert printTable([[1], [2], [3]])==None
  assert printTable([[1, 2], [3, 4]])==None
  assert printTable([])==None
output: def printTable(arr):
      if not arr:
          return None
      for row in arr:
          print(" ".join(map(str, row)))