input: Write a function to find the union of two given lists. Return the union as a list with unique elements appearing only once. If the given lists are empty, return an empty list.
  list1 = [1, 2, 3, 4, 5]
  list2 = [3, 4, 5, 6, 7]
  assert unionList(list1, list2)=={1, 2, 3, 4, 5, 6, 7}
  list1 = []
  list2 = []
  assert unionList(list1, list2)==set()
  list1 = [5, 5, 5]
  list2 = [5, 5]
  assert unionList(list1, list2)=={5}
  list1 = [1, 2, 3]
  list2 = [4, 5, 6]
  assert unionList(list1, list2)=={1, 2, 3, 4, 5, 6}
output: def unionList(list1, list2):
      return list(set(list1 + list2))