From the manual:
date arithmetic operations require complete dates and do not work with
incomplete dates such as '2006-07-00' or badly malformed dates.


mysql-test/r/func_time.result:
  Fix for bug #22229: Bug in DATE_ADD()
    - test result.
mysql-test/t/func_time.test:
  Fix for bug #22229: Bug in DATE_ADD()
    - test case.
sql/item_timefunc.cc:
  Fix for bug #22229: Bug in DATE_ADD()
    - Item_func_str_to_date::get_date() should return NULL if TIME_NO_ZERO_DATE 
      flag is set and year||month||day is 0.