Fix NPE in InstanceService.getAvailableJobInstances (#1952)

* Fix NPE in InstanceService.getAvailableJobInstances (#1950)

* use orElseGet
diff --git a/elasticjob-infra/elasticjob-registry-center/src/main/java/org/apache/shardingsphere/elasticjob/reg/zookeeper/ZookeeperRegistryCenter.java b/elasticjob-infra/elasticjob-registry-center/src/main/java/org/apache/shardingsphere/elasticjob/reg/zookeeper/ZookeeperRegistryCenter.java
index c414a0d..072ebfa 100644
--- a/elasticjob-infra/elasticjob-registry-center/src/main/java/org/apache/shardingsphere/elasticjob/reg/zookeeper/ZookeeperRegistryCenter.java
+++ b/elasticjob-infra/elasticjob-registry-center/src/main/java/org/apache/shardingsphere/elasticjob/reg/zookeeper/ZookeeperRegistryCenter.java
@@ -137,10 +137,7 @@
             return getDirectly(key);
         }
         Optional<ChildData> resultInCache = cache.get(key);
-        if (resultInCache.isPresent()) {
-            return null == resultInCache.get().getData() ? null : new String(resultInCache.get().getData(), StandardCharsets.UTF_8);
-        }
-        return getDirectly(key);
+        return resultInCache.map(v -> null == v.getData() ? null : new String(v.getData(), StandardCharsets.UTF_8)).orElseGet(() -> getDirectly(key));
     }
     
     private CuratorCache findCuratorCache(final String key) {
diff --git a/elasticjob-lite/elasticjob-lite-core/src/main/java/org/apache/shardingsphere/elasticjob/lite/internal/instance/InstanceService.java b/elasticjob-lite/elasticjob-lite-core/src/main/java/org/apache/shardingsphere/elasticjob/lite/internal/instance/InstanceService.java
index 6d316d9..0fb0c3b 100644
--- a/elasticjob-lite/elasticjob-lite-core/src/main/java/org/apache/shardingsphere/elasticjob/lite/internal/instance/InstanceService.java
+++ b/elasticjob-lite/elasticjob-lite-core/src/main/java/org/apache/shardingsphere/elasticjob/lite/internal/instance/InstanceService.java
@@ -70,7 +70,7 @@
         List<JobInstance> result = new LinkedList<>();
         for (String each : jobNodeStorage.getJobNodeChildrenKeys(InstanceNode.ROOT)) {
             JobInstance jobInstance = YamlEngine.unmarshal(jobNodeStorage.getJobNodeData(instanceNode.getInstancePath(each)), JobInstance.class);
-            if (serverService.isEnableServer(jobInstance.getServerIp())) {
+            if (null != jobInstance && serverService.isEnableServer(jobInstance.getServerIp())) {
                 result.add(new JobInstance(each));
             }
         }