Wrong result or protocol assertion failure upon update using user variable on spider table

INSTALL SONAME 'ha_spider';

SET spider_same_server_link = ON;

--eval create server s foreign data wrapper mysql options (host "127.0.0.1", database "test", user "root", port $MASTER_MYPORT)

CREATE TABLE t (f INT);

INSERT INTO t VALUES (1),(2);

SET @a = 4;

SET @a = NULL;

CREATE TABLE t_spider LIKE t;

ALTER TABLE t_spider ENGINE=SPIDER COMMENT = 'wrapper "mysql", srv "s", table "t"';

DELETE FROM t_spider WHERE f > 0 or f < @a;

SELECT * FROM t_spider;

Warning	138	Spider table params in COMMENT or CONNECTION strings have been deprecated and will be removed in a future release. Please use table options instead.

DELETE FROM t_spider WHERE f > 0 or f < @a;

SELECT * FROM t_spider;

f

1

2

                     3 Query    DELETE FROM t_spider WHERE f > 0 or f < @a

                     6 Connect  root@localhost on  using SSL/TLS

                     6 Query    set session time_zone = '+00:00';set @`spider_lc_./test/t` = '-74563cb22275-3ae990-./test/t_spider-'

                     6 Query    SET NAMES utf8mb4

                     6 Init DB  test

                     6 Query    set @old_lock_wait_timeout=@@session.lock_wait_timeout;set session lock_wait_timeout=1

                     6 Query    show table status from `test` like 't'

                     6 Query    set session lock_wait_timeout=@old_lock_wait_timeout

                     6 Query    set @old_lock_wait_timeout=@@session.lock_wait_timeout;set session lock_wait_timeout=1

                     6 Query    show index from `test`.`t`

                     6 Query    set session lock_wait_timeout=@old_lock_wait_timeout

                     6 Quit     

mariadbd: /data/bld/main-asan-ubsan/sql/protocol.cc:639: void Protocol::end_statement(): Assertion `0' failed.

260202 18:55:28 [ERROR] /share8t/bld/main-asan-ubsan/sql/mariadbd got signal 6 ;

#8  0x00007f1663645472 in __GI_abort () at ./stdlib/abort.c:79

#9  0x00007f1663645395 in __assert_fail_base (fmt=0x7f16637b9a90 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x5653fc267da0 "0", file=file@entry=0x5653fc265d00 "/data/bld/main-asan-ubsan/sql/protocol.cc", line=line@entry=639, function=function@entry=0x5653fc267cc0 "void Protocol::end_statement()") at ./assert/assert.c:92

#10 0x00007f1663653eb2 in __GI___assert_fail (assertion=0x5653fc267da0 "0", file=0x5653fc265d00 "/data/bld/main-asan-ubsan/sql/protocol.cc", line=639, function=0x5653fc267cc0 "void Protocol::end_statement()") at ./assert/assert.c:101

#11 0x00005653f7efe3b9 in Protocol::end_statement (this=this@entry=0x62c0000b08f8) at /data/bld/main-asan-ubsan/sql/protocol.cc:639

#12 0x00005653f856bde3 in dispatch_command (command=command@entry=COM_QUERY, thd=thd@entry=0x62c0000b0218, packet=<optimized out>, packet@entry=0x629000140219 "DELETE FROM t_spider WHERE f > 0 or f < @a", packet_length=packet_length@entry=42, blocking=blocking@entry=true) at /data/bld/main-asan-ubsan/sql/sql_parse.cc:2446

#13 0x00005653f857063b in do_command (thd=thd@entry=0x62c0000b0218, blocking=blocking@entry=true) at /data/bld/main-asan-ubsan/sql/sql_parse.cc:1432

#14 0x00005653f8dd7146 in do_handle_one_connection (connect=<optimized out>, connect@entry=0x6080000082b8, put_in_cache=put_in_cache@entry=true) at /data/bld/main-asan-ubsan/sql/sql_connect.cc:1503

#15 0x00005653f8dd82af in handle_one_connection (arg=0x6080000082b8) at /data/bld/main-asan-ubsan/sql/sql_connect.cc:1415

#16 0x00005653faa35dc1 in pfs_spawn_thread (arg=0x617000007798) at /data/bld/main-asan-ubsan/storage/perfschema/pfs.cc:2198

#17 0x00007f16636a81c4 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442

#18 0x00007f166372885c in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

Connection ID (thread ID): 3

Status: NOT_KILLED

Query (0x62d0000fa438): DELETE FROM t_spider WHERE f > 0 or f < @a