input: Write a function named construct_nested_loop that takes a list of lists as input and constructs a nested loop to print out each combination of elements from the sublists in a new line.
  assert construct_nested_loop([[1,2,3], [4,5,6], [7,8,9]]) == None
  # Output:
  # 1 4 7
  # 1 4 8
  # 1 4 9
  # 1 5 7
  # 1 5 8
  # 1 5 9
  # 1 6 7
  # 1 6 8
  # 1 6 9
  # 2 4 7
  # 2 4 8
  # 2 4 9
  # 2 5 7
  # 2 5 8
  # 2 5 9
  # 2 6 7
  # 2 6 8
  # 2 6 9
  # 3 4 7
  # 3 4 8
  # 3 4 9
  # 3 5 7
  # 3 5 8
  # 3 5 9
  # 3 6 7
  # 3 6 8
  # 3 6 9
  assert construct_nested_loop([]) == None
  # Output:
  # (No output as input list is empty)
output: def construct_nested_loop(lst):
      if not lst:
          return
      from itertools import product
      for combination in product(*lst):
          print(' '.join(map(str, combination)))