code: public static <T> StreamEx<T> of(Collection<? extends T> collection) {
          return of(collection.spliterator());
      }
docs: Returns a sequential {@code StreamEx} with given collection as its
  source.
  
  @param <T> the type of collection elements
  @param collection collection to create the stream of
  @return a sequential {@code StreamEx} over the elements in given
  collection
  @see Collection#stream()