A case expression with ROW arguments in THEN crashes

SELECT CASE WHEN TRUE THEN ROW(1,2) ELSE ROW(2,1) END;

#4  0x00007ffff7254c57 in __assert_fail () from /lib64/libc.so.6

#5  0x00005555563f114f in Type_handler_hybrid_field_type::aggregate_for_result

    (this=0x7fff84019b90, funcname=..., items=0x7fff84019bf8, nitems=2, 

    treat_bit_as_number=true) at /home/bar/maria-git/12.0/sql/sql_type.cc:1899

#6  0x000055555658f61e in Item_func_case::aggregate_then_and_else_arguments (

    this=0x7fff84019ae0, thd=0x7fff84000dc8, start=1)

    at /home/bar/maria-git/12.0/sql/item_cmpfunc.cc:3381

#7  0x000055555658f4cc in Item_func_case_searched::fix_length_and_dec (

    this=0x7fff84019ae0, thd=0x7fff84000dc8)

│     1891 bool Type_handler_hybrid_field_type::                               │

│     1892 aggregate_for_result(const LEX_CSTRING &funcname, Item **items, uint│

│     1893                      bool treat_bit_as_number)                      │

│     1894 {                                                                   │

│     1895   bool bit_and_non_bit_mixture_found= false;                        │

│     1896   uint32 max_display_length;                                        │

│     1897   if (!nitems || items[0]->result_type() == ROW_RESULT)             │

│     1898   {                                                                 │

│  >  1899     DBUG_ASSERT(0);                                                 │

│     1900     set_handler(&type_handler_null);                                │

│     1901     return true;                                                    │

│     1902   } 

SELECT CASE TRUE WHEN TRUE THEN ROW(1,2) ELSE ROW(2,1) END;

ERROR 1241 (21000): Operand should contain 1 column(s)