input: Write a function to find the union of two lists by combining them and converting the combined list to a set to remove duplicates. The function should return the union in the form of a set.
  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], [])=={1, 2, 3}
  assert unionList([], [])==set()
output: def unionList(list1, list2):
      return set(list1 + list2)