gaodayue opened a new issue #3520:
URL: https://github.com/apache/incubator-doris/issues/3520
**Describe the bug**
When input to hll function is null, BE crashes with the following stack
```
*** Aborted at 1588908360 (unix time) try "date -d @1588908360" if you are
using GNU date ***
PC: @ 0xe16f00 (unknown)
*** SIGSEGV (@0x0) received by PID 100031 (TID 0x7ff8805a0700) from PID 0;
stack trace: ***
@ 0x7ff8b1a675d0 (unknown)
@ 0xe16f00 (unknown)
@ 0xdc7578 doris::HllFunctions::hll_merge()
@ 0x14e5a53 doris::NewAggFnEvaluator::Update()
@ 0x1465ab6 doris::NewPartitionedAggregationNode::UpdateTuple()
@ 0x1470cef
doris::NewPartitionedAggregationNode::ProcessBatch<>()
@ 0x146b404 doris::NewPartitionedAggregationNode::open()
@ 0x1014d7b doris::PlanFragmentExecutor::open_internal()
@ 0x10154a4 doris::PlanFragmentExecutor::open()
@ 0xfa2637 doris::FragmentExecState::execute()
@ 0xfa4286 doris::FragmentMgr::exec_actual()
@ 0xfaa6e4
boost::detail::function::void_function_obj_invoker0<>::invoke()
@ 0xea8a58 doris::ThreadPool::work_thread()
@ 0x19ca0cd thread_proxy
@ 0x7ff8b1a5fdd5 start_thread
@ 0x7ff8b0e64ead __clone
```
**To Reproduce**
1) create a test table
```
CREATE TABLE `t1` (
`siteid` int(11) NULL COMMENT "",
`citycode` smallint(6) NULL COMMENT "",
`username` varchar(32) NULL COMMENT "",
`uv` hll HLL_UNION COMMENT "")
AGGREGATE KEY(`siteid`, `citycode`, `username`)
DISTRIBUTED BY HASH(`siteid`) BUCKETS 1
PROPERTIES (
"replication_num" = "3"
);
```
2) load some sample data
```
$ cat data.tsv
1 1 'jim' 2
2 1 'grace' 2
3 2 'tom' 2
4 3 'bush' 3
5 3 'helen' 3
$ curl -v --location-trusted -u user:pass -H
'columns:siteid,citycode,username,x,uv=hll_hash(x)' -T data.tsv -XPUT
http://localhost:8410/api/test/t1/_stream_load
```
3) make a query that could produce null input to hll function
```
mysql> select citycode, hll_union_agg(case when length(username) >= 100 then
uv end) from t3 group by citycode;
```
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