jdk11bug导致DefaultRheaIterator出现NullPointerException，是否考虑规避

[lfygh]

Describe the bug

java.lang.NullPointerException
    at com.alipay.sofa.jraft.util.BytesUtil$LexicographicByteArrayComparator.compare(BytesUtil.java:118)
    at com.alipay.sofa.jraft.util.BytesUtil$LexicographicByteArrayComparator.compare(BytesUtil.java:112)
    at com.alipay.sofa.jraft.util.BytesUtil.compare(BytesUtil.java:95)
    at com.alipay.sofa.jraft.rhea.client.DefaultRheaIterator.hasNext(DefaultRheaIterator.java:61)
    at com.betalpha.barbeyond.kv.RheaKVStoreBackend$1.hasNext(RheaKVStoreBackend.java:87)

Steps to reproduce

这个bug准确来说应该是jdk的，项目中使用的是11.0.15，存在这个问题，升级到jdk17后不存在这个问题，中间哪个版本修复的未知，如找到，忘告知。具体的现象如果将iterator转化为stream时，即使DefaultRheaIterator.hasNext()返回false，还会多调用一次。

复现步骤:

Iterator<Object> iterator = new Iterator<>() {
          @Override
          public boolean hasNext() {
              System.out.println("call hasNext");
              return false;
          }
          @Override
          public Object next() {
              return new Object();
          }
      };
    Stream<Object> stream1 = StreamSupport
            .stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false)
            .map(obj -> {return obj;});   //这行必须

    Stream<Object> stream2 = StreamSupport
            .stream(Spliterators.spliteratorUnknownSize(stream1.iterator(), Spliterator.ORDERED), false);

    System.out.println(stream2.collect(Collectors.toList()));

结果是：

call hasNext
call hasNext
[]

将上述代码的iterator替换为DefaultRheaIterator即可复现NPE。

看下是否有必要兼容下这种情况

Minimal yet complete reproducer code (or GitHub URL to code)

Environment

• SOFAJRaft version: jraft-rheakv-core-1.3.11.jar
• JVM version (e.g. java -version): 11.0.15

[fengjiachun]

要兼容的，是不是 cursorKey == null 导致的 NPE？欢迎提一个 PR 来兼容

[lfygh]

好的，稍后提一个pr