Window functions: crash when ORDER BY clause uses an expression

create table t1 (s1 int, s2 char(5));

insert into t1 values (1,'a');

insert into t1 values (null,null);

insert into t1 values (1,null);

insert into t1 values (null,'a');

insert into t1 values (2,'b');

insert into t1 values (-1,'');

select 

  *,

  ROW_NUMBER() OVER (order by s1),

  CUME_DIST() OVER (order by -s1) 

from t1;

  #1  0x0000555555c2a0ce in compare_order_elements (ord1=0x7fff580130e8, ord2=0x7fff580135e8) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_window.cc:243

  #2  0x0000555555c2a1c4 in compare_order_lists (part_list1=0x7fff58013158, part_list2=0x7fff58013658) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_window.cc:267

  #3  0x0000555555c2a5fc in compare_window_funcs_by_window_specs (win_func1=0x7fff580131b8, win_func2=0x7fff580136b8, arg=0x0) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_window.cc:393

  #4  0x0000555555c2dda0 in bubble_sort<Item_window_func> (list_to_sort=0x7fff58004fc8, sort_func=0x555555c2a511 <compare_window_funcs_by_window_specs(Item_window_func*, Item_window_func*, void*)>, arg=0x0) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_list.h:620

  #5  0x0000555555c2a796 in order_window_funcs_by_window_specs (win_func_list=0x7fff58004fc8) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_window.cc:465

  #6  0x0000555555c2b951 in Window_funcs_computation::setup (this=0x7fff58016860, thd=0x7fff58000b00, window_funcs=0x7fff58004fc8, tab=0x7fff58015700) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_window.cc:1878

  #7  0x0000555555ac5263 in JOIN::make_aggr_tables_info (this=0x7fff58013f10) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_select.cc:2670

  #8  0x0000555555ac2da6 in JOIN::optimize_inner (this=0x7fff58013f10) at /home/psergey/dev-git/10.2-window-funcs-r12/sql/sql_select.cc:2068

    int cmp= strcmp(item1->name, item2->name);