static <U extends Pair<Long, Double>> Bucket<U> of(U u) {
    return new Bucket<>(Collections.singletonList(u), u, u, u, u);
  }
this class is copied and modified from <a
href="https://github.com/ggalmazor/lt_downsampling_java8">...</a> project
library-udf/src/main/java/org/apache/iotdb/library/dprofile/util/Bucket.java