input: Write a function to print out all combinations of elements from three given lists, such that each combination is printed in a new line. If any list is empty, print "Invalid input".
  
  assert nested_loop_print([[1,2,3], [4,5,6], [7,8,9]])
  # Output should be:
  # 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 nested_loop_print([[], [4,5,6], [7,8,9]])=="Invalid input"
  assert nested_loop_print([[1,2,3], [], [7,8,9]])=="Invalid input"
  assert nested_loop_print([[1,2,3], [4,5,6], []])=="Invalid input"
  assert nested_loop_print([[], [], []])=="Invalid input"
output: def nested_loop_print(lists):
      if any(len(lst) == 0 for lst in lists):
          print("Invalid input")
          return
      for i in lists[0]:
          for j in lists[1]:
              for k in lists[2]:
                  print(i, j, k)