input: Write a function to find the common elements in two given lists. The function should return a list of common elements. If there are no common elements, it should return an empty list.
  
  assert find_common_elements([3, 9, 15, 21, 27], [21, 7, 13, 29, 31])==[21]
  assert find_common_elements([1, 2, 3], [4, 5, 6])==[]
  assert find_common_elements([10, 20, 30], [20, 30, 40])==[20, 30]
  assert find_common_elements([], [1, 2, 3])==[]
  assert find_common_elements([1, 2, 3], [])==[]
output: def find_common_elements(list1, list2):
      return list(set(list1) & set(list2))