java thrift返回List异常

对于下段代码：

 public List<String> hmget(String key, List<String> fields) throws org.apache.thrift.TException
  
 {
 
 			    JedisCluster jedis_cluster = RedisClusterProxy.get_jedis_cluster(); 
 
 String[] field_array = new String[fields.size()];
 
 			    fields.toArray(field_array);
 
 return jedis_cluster.hmget(key, field_array);
 
 } 

运行时遇到如下异常，原因是由于hmget返回的List含有null成员，导致thrift编码时异常： 20160415 14:55:39 ERROR org.apache.thrift.server.AbstractNonblockingServer$FrameBuffer.invoke(AbstractNonblockingServer.java:484) [Thread-0] Unexpected throwable while invoking! java.lang.NullPointerException         at org.apache.thrift.protocol.TBinaryProtocol.writeString(TBinaryProtocol.java:185)         at com.test.redis_cluster_proxy.RedisClusterProxyService$hmget_result$hmget_resultStandardScheme.write(RedisClusterProxyService.java:19434)         at com.test.redis_cluster_proxy.RedisClusterProxyService$hmget_result$hmget_resultStandardScheme.write(RedisClusterProxyService.java:1)         at com.test.redis_cluster_proxy.RedisClusterProxyService$hmget_result.write(RedisClusterProxyService.java:19337)         at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:53)         at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:39)         at org.apache.thrift.server.AbstractNonblockingServer$FrameBuffer.invoke(AbstractNonblockingServer.java:478)         at org.apache.thrift.server.TNonblockingServer.requestInvoke(TNonblockingServer.java:115)         at org.apache.thrift.server.AbstractNonblockingServer$AbstractSelectThread.handleRead(AbstractNonblockingServer.java:209)         at org.apache.thrift.server.TNonblockingServer$SelectAcceptThread.select(TNonblockingServer.java:198)         at org.apache.thrift.server.TNonblockingServer$SelectAcceptThread.run(TNonblockingServer.java:154) 当redis中没有相应的field时，hmget返回的List会包含null成员。解决此问题有两个办法： 1）保证查询的field一定存在 2）对hmget返回值做处理，null成员替换成空字符串""