input: Write a function that takes two lists as input and returns the union of these two lists by removing duplicates. If either list is empty, return the non-empty list as the result. If both lists are empty, return an empty list.
  
  assert unionList([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])=={1, 2, 3, 4, 5, 6, 7}
  assert unionList([], [3, 4, 5, 6, 7])=={3, 4, 5, 6, 7}
  assert unionList([1, 2, 3, 4, 5], [])=={1, 2, 3, 4, 5}
  assert unionList([], [])==set()
output: def unionList(list1, list2):
      if not list1:
          return set(list2)
      if not list2:
          return set(list1)
      return set(list1).union(set(list2))