[fix](group_concat) group_concat be crash in vectorized engine

be/src/vec/aggregate_functions/aggregate_function_group_concat.h

@@ -59,6 +59,7 @@ struct AggregateFunctionGroupConcatData {
     }
 
     std::string get() const { return data; }
+    bool is_null() const { return !inited; }
 
     void write(BufferWritable& buf) const {
         write_binary(data, buf);
@@ -132,8 +133,15 @@ class AggregateFunctionGroupConcat final
     }
 
     void insert_result_into(ConstAggregateDataPtr __restrict place, IColumn& to) const override {
-        std::string result = this->data(place).get();
-        static_cast<ColumnString&>(to).insert_data(result.c_str(), result.length());
+        bool is_null = this->data(place).is_null();
+        std::string result = is_null ? "" : this->data(place).get();
+        if (to.is_nullable()) {
+            static_cast<ColumnNullable&>(to).get_null_map_data().push_back(is_null);
+            static_cast<ColumnNullable&>(to).get_nested_column().insert_data(result.c_str(),
+                                                                             result.length());
+        } else {
+            static_cast<ColumnString&>(to).insert_data(result.c_str(), result.length());
+        }
     }
 };
 

regression-test/data/query/group_concat/test_group_concat_new_tbl.out

@@ -0,0 +1,7 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !select --
+1	\N
+
+-- !select --
+1	\N
+

regression-test/suites/query/group_concat/test_group_concat_new_tbl.groovy

@@ -0,0 +1,51 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+suite("test_group_concat_new_tbl", "issue_7288") {
+    def leftTableName = "group_concat_i7288_left"
+    def rightTableName = "group_concat_i7288_right"
+    sql "DROP TABLE IF EXISTS ${leftTableName}"
+    sql """
+        CREATE TABLE IF NOT EXISTS ${leftTableName} (
+            k1 int,
+            no varchar(10) NOT NULL
+        )
+        DISTRIBUTED BY HASH(k1) BUCKETS 1
+        PROPERTIES (
+          "replication_num" = "1"
+        )
+    """
+    sql "INSERT INTO ${leftTableName} values(1,'test')"
+
+    sql "DROP TABLE IF EXISTS ${rightTableName}"
+    sql """
+        CREATE TABLE IF NOT EXISTS ${rightTableName} (
+            k1 int,
+            no varchar(10) NOT NULL
+        )
+        DISTRIBUTED BY HASH(k1) BUCKETS 1
+        PROPERTIES (
+          "replication_num" = "1"
+        )
+    """
+
+    sql "set enable_vectorized_engine=true"
+    qt_select(""" select l.k1, group_concat(r.no) from ${leftTableName} l left join ${rightTableName} r on l.k1=r.k1 group by l.k1; """);
+
+    sql "set enable_vectorized_engine=false"
+    qt_select(""" select l.k1, group_concat(r.no) from ${leftTableName} l left join ${rightTableName} r on l.k1=r.k1 group by l.k1; """);
+}