Server crash in Charset::charset / Item_func_natural_sort_key::val_str

CREATE TABLE t (f CHAR(1));

INSERT INTO t VALUES ('a'),('b');

SELECT GET_LOCK(f,1) FROM t;

SELECT NATURAL_SORT_KEY(RELEASE_LOCK(f)) FROM t;

# Cleanup

DROP TABLE t;

#3  <signal handler called>

#4  0x0000555e3d51b0eb in Charset::charset (this=0x0) at /data/src/natural-sort-asan/sql/sql_string.h:156

#5  0x0000555e3e2a458d in Item_func_natural_sort_key::val_str (this=0x6290000e6ad8, out=0x7f5e3a719610) at /data/src/natural-sort-asan/sql/item_strfunc.cc:5509

#6  0x0000555e3de3febc in Type_handler::Item_send_str (this=0x555e41a9a140 <type_handler_varchar>, item=0x6290000e6ad8, protocol=0x62b00007e870, buf=0x7f5e3a7195e0) at /data/src/natural-sort-asan/sql/sql_type.cc:7455

#7  0x0000555e3dc39f16 in Type_handler_string_result::Item_send (this=0x555e41a9a140 <type_handler_varchar>, item=0x6290000e6ad8, protocol=0x62b00007e870, buf=0x7f5e3a7195e0) at /data/src/natural-sort-asan/sql/sql_type.h:5440

#8  0x0000555e3d45c6e0 in Item::send (this=0x6290000e6ad8, protocol=0x62b00007e870, buffer=0x7f5e3a7195e0) at /data/src/natural-sort-asan/sql/item.h:1227

#9  0x0000555e3d5148db in Protocol::send_result_set_row (this=0x62b00007e870, row_items=0x6290000e6610) at /data/src/natural-sort-asan/sql/protocol.cc:1327

#10 0x0000555e3d6bcaa0 in select_send::send_data (this=0x6290000e7c70, items=...) at /data/src/natural-sort-asan/sql/sql_class.cc:3072

#11 0x0000555e3d9cfecf in select_result_sink::send_data_with_check (this=0x6290000e7c70, items=..., u=0x62b0000825f0, sent=0) at /data/src/natural-sort-asan/sql/sql_class.h:5631

#12 0x0000555e3d98aeac in end_send (join=0x6290000e7ca0, join_tab=0x6290000e9348, end_of_records=false) at /data/src/natural-sort-asan/sql/sql_select.cc:22284

#13 0x0000555e3d982eab in evaluate_join_record (join=0x6290000e7ca0, join_tab=0x6290000e8f98, error=0) at /data/src/natural-sort-asan/sql/sql_select.cc:21277

#14 0x0000555e3d981801 in sub_select (join=0x6290000e7ca0, join_tab=0x6290000e8f98, end_of_records=false) at /data/src/natural-sort-asan/sql/sql_select.cc:21054

#15 0x0000555e3d97f9f2 in do_select (join=0x6290000e7ca0, procedure=0x0) at /data/src/natural-sort-asan/sql/sql_select.cc:20601

#16 0x0000555e3d90bf51 in JOIN::exec_inner (this=0x6290000e7ca0) at /data/src/natural-sort-asan/sql/sql_select.cc:4735

#17 0x0000555e3d909432 in JOIN::exec (this=0x6290000e7ca0) at /data/src/natural-sort-asan/sql/sql_select.cc:4513

#18 0x0000555e3d90d98d in mysql_select (thd=0x62b00007e288, tables=0x6290000e6c60, fields=..., conds=0x0, og_num=0, order=0x0, group=0x0, having=0x0, proc_param=0x0, select_options=2147748608, result=0x6290000e7c70, unit=0x62b0000825f0, select_lex=0x6290000e6370) at /data/src/natural-sort-asan/sql/sql_select.cc:4991

#19 0x0000555e3d8dddef in handle_select (thd=0x62b00007e288, lex=0x62b000082528, result=0x6290000e7c70, setup_tables_done_option=0) at /data/src/natural-sort-asan/sql/sql_select.cc:545

#20 0x0000555e3d80ae89 in execute_sqlcom_select (thd=0x62b00007e288, all_tables=0x6290000e6c60) at /data/src/natural-sort-asan/sql/sql_parse.cc:6261

#21 0x0000555e3d7f98c1 in mysql_execute_command (thd=0x62b00007e288, is_called_from_prepared_stmt=false) at /data/src/natural-sort-asan/sql/sql_parse.cc:3946

#22 0x0000555e3d81614c in mysql_parse (thd=0x62b00007e288, rawbuf=0x6290000e62a8 "SELECT NATURAL_SORT_KEY(RELEASE_LOCK(f)) FROM t", length=47, parser_state=0x7f5e3a71b9a0) at /data/src/natural-sort-asan/sql/sql_parse.cc:8036

#23 0x0000555e3d7ec176 in dispatch_command (command=COM_QUERY, thd=0x62b00007e288, packet=0x62900025d289 "", packet_length=47, blocking=true) at /data/src/natural-sort-asan/sql/sql_parse.cc:1896

#24 0x0000555e3d7e8e9a in do_command (thd=0x62b00007e288, blocking=true) at /data/src/natural-sort-asan/sql/sql_parse.cc:1404

#25 0x0000555e3dc81e7b in do_handle_one_connection (connect=0x61100000a488, put_in_cache=true) at /data/src/natural-sort-asan/sql/sql_connect.cc:1418

#26 0x0000555e3dc81707 in handle_one_connection (arg=0x61100000a348) at /data/src/natural-sort-asan/sql/sql_connect.cc:1312

#27 0x0000555e3e81b96b in pfs_spawn_thread (arg=0x618000005508) at /data/src/natural-sort-asan/storage/perfschema/pfs.cc:2201

#28 0x00007f5e44085609 in start_thread (arg=<optimized out>) at pthread_create.c:477

#29 0x00007f5e43c58293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95