From fc39ce8673b5af8c6bf6a1e6c2f0756d033e62c7 Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Wed, 26 Dec 2018 07:12:14 +0300
Subject: [PATCH] Fixed UB #3926

---
 dbms/src/AggregateFunctions/AggregateFunctionGroupArray.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/dbms/src/AggregateFunctions/AggregateFunctionGroupArray.h b/dbms/src/AggregateFunctions/AggregateFunctionGroupArray.h
index 094cae05615..c6fb68c86dd 100644
--- a/dbms/src/AggregateFunctions/AggregateFunctionGroupArray.h
+++ b/dbms/src/AggregateFunctions/AggregateFunctionGroupArray.h
@@ -121,8 +121,11 @@ public:
 
         offsets_to.push_back(offsets_to.back() + size);
 
-        typename ColumnVector<T>::Container & data_to = static_cast<ColumnVector<T> &>(arr_to.getData()).getData();
-        data_to.insert(this->data(place).value.begin(), this->data(place).value.end());
+        if (size)
+        {
+            typename ColumnVector<T>::Container & data_to = static_cast<ColumnVector<T> &>(arr_to.getData()).getData();
+            data_to.insert(this->data(place).value.begin(), this->data(place).value.end());
+        }
     }
 
     bool allocatesMemoryInArena() const override