Crash when pushing condition into view defined as union

create table t1 (

   n int,

   lv varchar(31) charset latin1,

   mv varchar(31) charset utf8mb3

) engine=myisam;

insert into t1 values (1,'aa','xxx'), ('2','bb','yyy'), (3,'cc','zzz');

create view v1 as

select case when n=1 then lv when n=2 then mv else NULL end as r from t1 

union

select 'a'; 

prepare stmt from "select * from v1 where r < 'x'";

execute stmt;

sql/signal_handler.cc:238(handle_fatal_signal)[0x5619d7043b23]

/lib64/libpthread.so.0(+0xf890)[0x7f08d7e88890]

sql/item.cc:3411(Item_field::used_tables() const)[0x5619d706f433]

sql/item.h:5171(Used_tables_and_const_cache::used_tables_and_const_cache_join(Item const*))[0x5619d6c63f7d]

sql/item.h:5178(Used_tables_and_const_cache::used_tables_and_const_cache_update_and_join(Item*))[0x5619d6c64002]

sql/item.h:5187(Used_tables_and_const_cache::used_tables_and_const_cache_update_and_join(unsigned int, Item**))[0x5619d6c64044]

sql/item_func.h:161(Item_func::update_used_tables())[0x5619d6c656c0]

sql/item.h:7677(Item_direct_ref_to_item::update_used_tables())[0x5619d708c6eb]

sql/item.h:5177(Used_tables_and_const_cache::used_tables_and_const_cache_update_and_join(Item*))[0x5619d6c63fef]

sql/item.h:5187(Used_tables_and_const_cache::used_tables_and_const_cache_update_and_join(unsigned int, Item**))[0x5619d6c64044]

sql/item_func.h:161(Item_func::update_used_tables())[0x5619d6c656c0]

sql/sql_lex.cc:4670(st_select_lex::update_used_tables())[0x5619d6cc64b1]

sql/sql_select.cc:1927(JOIN::optimize_inner())[0x5619d6d44b40]

sql/sql_select.cc:1690(JOIN::optimize())[0x5619d6d43f6a]

sql/sql_union.cc:1490(st_select_lex_unit::optimize())[0x5619d6e0f9b2]

sql/sql_derived.cc:995(mysql_derived_optimize(THD*, LEX*, TABLE_LIST*))[0x5619d6c9f894]

sql/sql_derived.cc:200(mysql_handle_single_derived(LEX*, TABLE_LIST*, unsigned int))[0x5619d6c9d4c4]

sql/sql_select.cc:2180(JOIN::optimize_inner())[0x5619d6d45cd9]

sql/sql_select.cc:1690(JOIN::optimize())[0x5619d6d43f6a]

sql/sql_select.cc:4797(mysql_select(THD*, TABLE_LIST*, unsigned int, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, unsigned long long, select_result*, st_select_lex_unit*, st_select_lex*))[0x5619d6d4f817]

sql/sql_select.cc:454(handle_select(THD*, LEX*, select_result*, unsigned long))[0x5619d6d3ec32]

sql/sql_parse.cc:6463(execute_sqlcom_select(THD*, TABLE_LIST*))[0x5619d6d02e00]

sql/sql_parse.cc:3966(mysql_execute_command(THD*))[0x5619d6cf97c3]

sql/sql_prepare.cc:5024(Prepared_statement::execute(String*, bool))[0x5619d6d2863c]

sql/sql_prepare.cc:4493(Prepared_statement::execute_loop(String*, bool, unsigned char*, unsigned char*))[0x5619d6d269e3]

sql/sql_prepare.cc:3578(mysql_sql_stmt_execute(THD*))[0x5619d6d242c3]

sql/sql_parse.cc:3983(mysql_execute_command(THD*))[0x5619d6cf9808]

sql/sql_parse.cc:7998(mysql_parse(THD*, char*, unsigned int, Parser_state*, bool, bool))[0x5619d6d06d66]

sql/sql_parse.cc:1860(dispatch_command(enum_server_command, THD*, char*, unsigned int, bool, bool))[0x5619d6cf3383]

sql/sql_parse.cc:1379(do_command(THD*))[0x5619d6cf1ba7]

sql/sql_connect.cc:1420(do_handle_one_connection(CONNECT*))[0x5619d6e8bf11]

sql/sql_connect.cc:1325(handle_one_connection)[0x5619d6e8bc6d]

perfschema/pfs.cc:1871(pfs_spawn_thread)[0x5619d73ed20c]

/lib64/libpthread.so.0(+0x80a4)[0x7f08d7e810a4]

/lib64/libc.so.6(clone+0x6d)[0x7f08d72b904d]

Trying to get some variables.

Some pointers may be invalid and cause the dump to abort.

Query (0x7f08c00145b8): select * from v1 where r < 'x'