input: Write a function to construct a nested loop in Python that prints out the elements from the input arrays in a new line. The function should take a list of lists as input and print each combination of elements from the sublists. If the input is empty, the function should not print anything.
  assert nested_loops([[1,2,3], [4,5,6], [7,8,9]])==None
  assert nested_loops([])==None
output: def nested_loops(lists):
      if not lists:
          return
      for i in lists[0]:
          if len(lists) == 1:
              print(i)
          else:
              for j in nested_loops(lists[1:]):
                  print(i, j)