docs: public static <T> List<T> getLeftDiff(List<T> list1, List<T> list2) {
          if (isEmpty(list2)) {
              return list1;
          }
          List<T> list = new ArrayList<T>();
          if (isNotEmpty(list1)) {
              for (T o : list1) {
                  if (!list2.contains(o)) {
                      list.add(o);
                  }
              }
          }
          return list;
      }