Server crashes in Compare_identifiers::operator or in my_strcasecmp_utf8 upon ADD PERIOD IF NOT EXISTS with empty name

ALTER TABLE t ADD PERIOD IF NOT EXISTS FOR `` (s,e);

#3  <signal handler called>

#4  0x000056225dec77ca in Compare_identifiers::operator() (this=0x7fd1a807a41f, a=..., b=...) at /data/src/10.4/sql/vers_string.h:42

#5  0x000056225ded034f in Lex_cstring_with_compare<Compare_identifiers>::streq (this=0x7fd198005e80, b=...) at /data/src/10.4/sql/vers_string.h:91

#6  0x000056225e0ec019 in LEX::add_period (this=0x7fd198004960, name=..., start=..., end=...) at /data/src/10.4/sql/sql_lex.h:4363

#7  0x000056225e0bd18f in MYSQLparse (thd=0x7fd198000b00) at /data/src/10.4/sql/sql_yacc.yy:6585

#8  0x000056225de49bd4 in parse_sql (thd=0x7fd198000b00, parser_state=0x7fd1a807c180, creation_ctx=0x0, do_pfs_digest=true) at /data/src/10.4/sql/sql_parse.cc:10247

#9  0x000056225de449c3 in mysql_parse (thd=0x7fd198000b00, rawbuf=0x7fd198015620 "ALTER TABLE t ADD PERIOD IF NOT EXISTS FOR `` (s,e)", length=51, parser_state=0x7fd1a807c180, is_com_multi=false, is_next_command=false) at /data/src/10.4/sql/sql_parse.cc:8157

#10 0x000056225de301a5 in dispatch_command (command=COM_QUERY, thd=0x7fd198000b00, packet=0x7fd19800a781 "ALTER TABLE t ADD PERIOD IF NOT EXISTS FOR `` (s,e)", packet_length=51, is_com_multi=false, is_next_command=false) at /data/src/10.4/sql/sql_parse.cc:1829

#11 0x000056225de2e98b in do_command (thd=0x7fd198000b00) at /data/src/10.4/sql/sql_parse.cc:1358

#12 0x000056225dfa8703 in do_handle_one_connection (connect=0x562261131340) at /data/src/10.4/sql/sql_connect.cc:1399

#13 0x000056225dfa8474 in handle_one_connection (arg=0x562261131340) at /data/src/10.4/sql/sql_connect.cc:1302

#14 0x000056225e49e031 in pfs_spawn_thread (arg=0x5622612239b0) at /data/src/10.4/storage/perfschema/pfs.cc:1862

#15 0x00007fd1afbd9494 in start_thread (arg=0x7fd1a807d700) at pthread_create.c:333

#16 0x00007fd1adfbf93f in clone () from /lib/x86_64-linux-gnu/libc.so.6

#2  <signal handler called>

#3  my_strcasecmp_utf8 (cs=<optimized out>, s=0x0, t=0x7f22140127e8 "") at /data/src/10.4/strings/ctype-utf8.c:5109

#4  0x000056491b01406e in operator() (this=<optimized out>, a=..., b=<synthetic pointer>) at /data/src/10.4/sql/vers_string.h:44

#5  streq (b=<synthetic pointer>, this=0x7f2214005b68) at /data/src/10.4/sql/vers_string.h:91

#6  LEX::add_period (this=0x7f2214004648, name=..., start=..., end=...) at /data/src/10.4/sql/sql_lex.h:4363

#7  0x000056491aff9c8e in MYSQLparse (thd=0x7f22140009a8) at /data/src/10.4/sql/sql_yacc.yy:6585

#8  0x000056491ae69945 in parse_sql (thd=thd@entry=0x7f22140009a8, parser_state=parser_state@entry=0x7f22301bf1d0, creation_ctx=creation_ctx@entry=0x0, do_pfs_digest=do_pfs_digest@entry=true) at /data/src/10.4/sql/sql_parse.cc:10247

#9  0x000056491ae69bf6 in mysql_parse (thd=thd@entry=0x7f22140009a8, rawbuf=<optimized out>, length=51, parser_state=parser_state@entry=0x7f22301bf1d0, is_com_multi=is_com_multi@entry=false, is_next_command=is_next_command@entry=false) at /data/src/10.4/sql/sql_parse.cc:8157

#10 0x000056491ae6c5a2 in dispatch_command (command=command@entry=COM_QUERY, thd=thd@entry=0x7f22140009a8, packet=packet@entry=0x7f2214009b59 "ALTER TABLE t ADD PERIOD IF NOT EXISTS FOR `` (s,e)", packet_length=packet_length@entry=51, is_com_multi=is_com_multi@entry=false, is_next_command=is_next_command@entry=false) at /data/src/10.4/sql/sql_parse.cc:1829

#11 0x000056491ae6d9f7 in do_command (thd=0x7f22140009a8) at /data/src/10.4/sql/sql_parse.cc:1358

#12 0x000056491af47f9c in do_handle_one_connection (connect=connect@entry=0x56491d3c8628) at /data/src/10.4/sql/sql_connect.cc:1399

#13 0x000056491af48104 in handle_one_connection (arg=arg@entry=0x56491d3c8628) at /data/src/10.4/sql/sql_connect.cc:1302

#14 0x000056491b2647b4 in pfs_spawn_thread (arg=0x56491d3fc9e8) at /data/src/10.4/storage/perfschema/pfs.cc:1862

#15 0x00007f223751d494 in start_thread (arg=0x7f22301c0700) at pthread_create.c:333

#16 0x00007f223590393f in clone () from /lib/x86_64-linux-gnu/libc.so.6