array_agg(DISTINCT) caused a segmentation fault

Hi,

In the current master branch, with enable_presorted_aggregate = on,
I got a segmentation fault when executing the following query.
OTOH, the query didn't cause a segmentation fault
when enable_presorted_aggregate was disabled.

=# SELECT array_agg(distinct val) FROM (SELECT NULL AS val FROM generate_series(1, 2)) hoge;

LOG:  server process (PID 76507) was terminated by signal 11: Segmentation fault: 11
DETAIL:  Failed process was running: SELECT array_agg(distinct val) FROM (SELECT NULL AS val FROM generate_series(1, 2)) hoge;


The backtrace extracted from the core file is;

* thread #1
   * frame #0: 0x000000010815807d postgres`toast_raw_datum_size(value=0) at detoast.c:550:6
     frame #1: 0x000000010891d31b postgres`texteq(fcinfo=0x00007ff7b7dc06b8) at varlena.c:1804:10
     frame #2: 0x0000000108975607 postgres`FunctionCall2Coll(flinfo=0x00007fd46900e0d8, collation=100, arg1=0, arg2=0) at fmgr.c:1148:11
     frame #3: 0x000000010846bee0 postgres`ExecEvalPreOrderedDistinctSingle(aggstate=0x00007fd46900c548, pertrans=0x00007fd46900dff0) at execExprInterp.c:4253:17
     frame #4: 0x00000001084668a6 postgres`ExecInterpExpr(state=0x00007fd46908cab8, econtext=0x00007fd46900c970, isnull=0x00007ff7b7dc09d7) at execExprInterp.c:1772:8
     frame #5: 0x000000010849804b postgres`ExecEvalExprSwitchContext(state=0x00007fd46908cab8, econtext=0x00007fd46900c970, isNull=0x00007ff7b7dc09d7) at executor.h:344:13
     frame #6: 0x00000001084974ff postgres`advance_aggregates(aggstate=0x00007fd46900c548) at nodeAgg.c:823:2
     frame #7: 0x0000000108496ff1 postgres`agg_retrieve_direct(aggstate=0x00007fd46900c548) at nodeAgg.c:2446:6
     frame #8: 0x000000010849428b postgres`ExecAgg(pstate=0x00007fd46900c548) at nodeAgg.c:2171:14
     frame #9: 0x0000000108480502 postgres`ExecProcNodeFirst(node=0x00007fd46900c548) at execProcnode.c:464:9
     frame #10: 0x0000000108477f42 postgres`ExecProcNode(node=0x00007fd46900c548) at executor.h:262:9
     frame #11: 0x0000000108473351 postgres`ExecutePlan(estate=0x00007fd46900c318, planstate=0x00007fd46900c548, use_parallel_mode=false, operation=CMD_SELECT, sendTuples=true, numberTuples=0, direction=ForwardScanDirection, dest=0x00007fd46908a4e0, execute_once=true) at execMain.c:1633:10
     frame #12: 0x000000010847320b postgres`standard_ExecutorRun(queryDesc=0x00007fd469009318, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:364:3
     frame #13: 0x0000000108472fc2 postgres`ExecutorRun(queryDesc=0x00007fd469009318, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:308:3
     frame #14: 0x0000000108752794 postgres`PortalRunSelect(portal=0x00007fd469031718, forward=true, count=0, dest=0x00007fd46908a4e0) at pquery.c:924:4
     frame #15: 0x0000000108752179 postgres`PortalRun(portal=0x00007fd469031718, count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x00007fd46908a4e0, altdest=0x00007fd46908a4e0, qc=0x00007ff7b7dc0df0) at pquery.c:768:18
     frame #16: 0x000000010874d5a2 postgres`exec_simple_query(query_string="SELECT array_agg(distinct val) FROM (SELECT NULL AS val FROM generate_series(1, 2)) hoge;") at postgres.c:1237:10
     frame #17: 0x000000010874c6de postgres`PostgresMain(dbname="postgres", username="postgres") at postgres.c:4565:7
     frame #18: 0x000000010865c7c2 postgres`BackendRun(port=0x00007fd468404080) at postmaster.c:4461:2
     frame #19: 0x000000010865a09c postgres`BackendStartup(port=0x00007fd468404080) at postmaster.c:4189:3
     frame #20: 0x0000000108657a7e postgres`ServerLoop at postmaster.c:1779:6
     frame #21: 0x00000001086566d0 postgres`PostmasterMain(argc=3, argv=0x0000600001635260) at postmaster.c:1463:11
     frame #22: 0x0000000108506b27 postgres`main(argc=3, argv=0x0000600001635260) at main.c:200:3
     frame #23: 0x000000011202552e dyld`start + 462

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION