EXPLAIN FORMAT=JSON crashes on a query with "Distinct" optimzation

create table ten(a int);

insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);

create table twenty (a int, filler char(200), key(a));

insert into twenty select A.a + B.a* 10, 'AAAAAAAAAAAAAAAAAAAA' from ten A, ten B where B.a in (0,1);

explain format=json select distinct A.a from ten A, twenty B where A.a+B.a> 0; 

  #0  0x00007ffff63b3425 in __GI_raise (sig=<optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64

  #1  0x00007ffff63b6b8b in __GI_abort () at abort.c:91

  #2  0x00007ffff63ac0ee in __assert_fail_base (fmt=<optimized out>, assertion=0x11010c0 "0", file=0x1101218 "/home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc", line=<optimized out>, function=<optimized out>) at assert.c:94

  #3  0x00007ffff63ac192 in __GI___assert_fail (assertion=0x11010c0 "0", file=0x1101218 "/home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc", line=1304, function=0x1101ca0 "void Explain_table_access::tag_to_json(Json_writer*, explain_extra_tag)") at assert.c:103

  #4  0x00000000007e31cf in Explain_table_access::tag_to_json (this=0x7fff940099f8, writer=0x7ffff016f010, tag=ET_DISTINCT) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc:1304

  #5  0x00000000007e3b20 in Explain_table_access::print_explain_json (this=0x7fff940099f8, query=0x7fff940091b0, writer=0x7ffff016f010, is_analyze=false, fs_tracker=0x0) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc:1491

  #6  0x00000000007e1e2f in Explain_basic_join::print_explain_json_interns (this=0x7fff94009320, query=0x7fff940091b0, writer=0x7ffff016f010, is_analyze=false, first_table_sort=0x0) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc:887

  #7  0x00000000007e1cb4 in Explain_select::print_explain_json (this=0x7fff94009320, query=0x7fff940091b0, writer=0x7ffff016f010, is_analyze=false) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc:850

  #8  0x00000000007dfd8e in Explain_query::print_explain_json (this=0x7fff940091b0, output=0x7fff94006850, is_analyze=false) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_explain.cc:221

  #9  0x0000000000688a7a in execute_sqlcom_select (thd=0x306cb50, all_tables=0x7fff94005648) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_parse.cc:5733

  #10 0x000000000067f102 in mysql_execute_command (thd=0x306cb50) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_parse.cc:2926

  #11 0x000000000068c377 in mysql_parse (thd=0x306cb50, rawbuf=0x7fff940053c8 "explain format=json select distinct A.a from ten A, twenty B where A.a+B.a> 0", length=77, parser_state=0x7ffff01700c0) at /home/psergey/dev-git/10.1-explain-analyze-cp/sql/sql_parse.cc:7165

+------+-------------+-------+-------+---------------+------+---------+------+------+------------------------------------------------------------------------+

| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra                                                                  |

+------+-------------+-------+-------+---------------+------+---------+------+------+------------------------------------------------------------------------+

|    1 | SIMPLE      | A     | ALL   | NULL          | NULL | NULL    | NULL |   10 | Using temporary                                                        |

|    1 | SIMPLE      | B     | index | NULL          | a    | 5       | NULL |   20 | Using where; Using index; Distinct; Using join buffer (flat, BNL join) |

+------+-------------+-------+-------+---------------+------+---------+------+------+------------------------------------------------------------------------+