Crash during instant ADD COLUMN with long DEFAULT value

create table t1(f1 int, f2 int not null)engine=innodb;

insert into t1 values(1, 2);

alter table t1 add column f3 int not null default 4, algorithm=instant;

alter table t1 add column f4 blob not null default repeat('a', 9999), algorithm=instant;

check table t1;

drop table t1;

btr/btr0cur.cc:4679: dberr_t btr_cur_pessimistic_update(ulint, btr_cur_t*, ulint**, mem_heap_t**, mem_heap_t*, big_rec_t**, upd_t*, ulint, que_thr_t*, trx_id_t, mtr_t*): Assertion `flags & BTR_KEEP_POS_FLAG' failed.