code: public static DoubleStreamEx of(Collection<Double> collection) {
          return seq(collection.stream().mapToDouble(Double::doubleValue));
      }
docs: Returns a sequential ordered {@code DoubleStreamEx} whose elements are
  the unboxed elements of supplied collection.
  
  @param collection the collection to create the stream from.
  @return the new stream
  @see Collection#stream()