input: Write a function to find the union of two lists. The union should contain all unique elements from both lists. If either of the lists is empty, the function should return the other list. If both lists are empty, it should return an empty list.
  def unionList(list1, list2):
      if not list1:
          return list2
      if not list2:
          return list1
      return set(list1 + list2)
  assert unionList([1, 2, 3, 4, 5], [3, 4, 5, 6, 7])=={1, 2, 3, 4, 5, 6, 7}
  assert unionList([1, 2, 3], [])==[1, 2, 3]
  assert unionList([], [4, 5, 6])==[4, 5, 6]
  assert unionList([], [])==[]
output: def unionList(list1, list2):
      if not list1:
          return list2
      if not list2:
          return list1
      return list(set(list1 + list2))