getShardingInfo Report NullPointerException

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Which version of ElasticJob did you use?

elasticjob 3.0.4

Expected behavior

Actual behavior

java.lang.NullPointerException: null
	at java.io.StringReader.<init>(StringReader.java:50)
	at org.yaml.snakeyaml.reader.StreamReader.<init>(StreamReader.java:57)
	at org.yaml.snakeyaml.Yaml.loadAs(Yaml.java:473)
	at org.apache.shardingsphere.elasticjob.infra.yaml.YamlEngine.unmarshal(YamlEngine.java:54)
	at org.apache.shardingsphere.elasticjob.lite.lifecycle.internal.statistics.ShardingStatisticsAPIImpl.getShardingInfo(ShardingStatisticsAPIImpl.java:64)
	at org.apache.shardingsphere.elasticjob.lite.lifecycle.internal.statistics.ShardingStatisticsAPIImpl.getShardingInfo(ShardingStatisticsAPIImpl.java:47)

Reason analyze (If you can)

private ShardingInfo getShardingInfo(final String jobName, final String item) {
       //Obtain the instance. However, the instance may be an offline instance.
        String instanceId = regCenter.get(jobNodePath.getShardingNodePath(item, "instance"));
        if (null != instanceId) {
            // The online instance data is obtained from the instance node based on the offline instance. In this case, the returned result is null.
            JobInstance jobInstance = YamlEngine.unmarshal(regCenter.get(jobNodePath.getInstanceNodePath(instanceId)), JobInstance.class);
            result.setServerIp(jobInstance.getServerIp());
            result.setInstanceId(jobInstance.getJobInstanceId());
        }
    }

Steps to reproduce the behavior.

Example codes for reproduce this issue (such as a github link).

[linghengqian]

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