input: Write a function to find the common elements between two given lists. Return a list containing all common elements. If either list is empty then return an empty list.
  assert find_common_elements([1, 2, 3], [2, 3, 4])==[2, 3]
  assert find_common_elements([1, 2, 3], [4, 5, 6])==[]
  assert find_common_elements([1, 2, 3], [])==[]
  assert find_common_elements([], [4, 5, 6])==[]
  assert find_common_elements([], [])==[]
output: def find_common_elements(list1, list2):
      if not list1 or not list2:
          return []
      return list(set(list1) & set(list2))