gcol.gcol_select_myisam fails in buildbot with valgrind (Conditional jump or move depends on uninitialised value)

gcol.gcol_select_myisam                  w2 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2016-12-22 11:43:07

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==12875== Thread 11:

==12875== Conditional jump or move depends on uninitialised value(s)

==12875==    at 0x9BE419: Item_func_concat::val_str(String*) (item_strfunc.cc:631)

==12875==    by 0x93ADD6: Item::save_in_field(Field*, bool) (item.cc:6278)

==12875==    by 0x7AD13E: TABLE::update_virtual_fields(enum_vcol_update_mode) (table.cc:7354)

==12875==    by 0x91C9F8: handler::ha_index_first(unsigned char*) (handler.cc:2725)

==12875==    by 0xA7F133: get_index_min_value(TABLE*, st_table_ref*, Item_field*, unsigned int, unsigned int) (opt_sum.cc:117)

==12875==    by 0xA7FB0B: opt_sum_query(THD*, List<TABLE_LIST>&, List<Item>&, Item*) (opt_sum.cc:403)

==12875==    by 0x6E3C25: JOIN::optimize_inner() (sql_select.cc:1393)

==12875==    by 0x6E2B05: JOIN::optimize() (sql_select.cc:1076)

==12875==    by 0x6EB535: mysql_select(THD*, TABLE_LIST*, unsigned int, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, unsigned long long, select_result*, st_select_lex_unit*, st_select_lex*) (sql_select.cc:3570)

==12875==    by 0x6E055F: handle_select(THD*, LEX*, select_result*, unsigned long) (sql_select.cc:373)

==12875==    by 0x6AC2D9: execute_sqlcom_select(THD*, TABLE_LIST*) (sql_parse.cc:6399)

==12875==    by 0x6A1AE4: mysql_execute_command(THD*) (sql_parse.cc:3423)

==12875== Conditional jump or move depends on uninitialised value(s)

==12875==    at 0x9BE533: Item_func_concat::val_str(String*) (item_strfunc.cc:646)

==12875==    by 0x93ADD6: Item::save_in_field(Field*, bool) (item.cc:6278)

==12875==    by 0x7AD13E: TABLE::update_virtual_fields(enum_vcol_update_mode) (table.cc:7354)

==12875==    by 0x91C9F8: handler::ha_index_first(unsigned char*) (handler.cc:2725)

==12875==    by 0xA7F133: get_index_min_value(TABLE*, st_table_ref*, Item_field*, unsigned int, unsigned int) (opt_sum.cc:117)

==12875==    by 0xA7FB0B: opt_sum_query(THD*, List<TABLE_LIST>&, List<Item>&, Item*) (opt_sum.cc:403)

==12875==    by 0x6E3C25: JOIN::optimize_inner() (sql_select.cc:1393)

==12875==    by 0x6E2B05: JOIN::optimize() (sql_select.cc:1076)

==12875==    by 0x6EB535: mysql_select(THD*, TABLE_LIST*, unsigned int, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, unsigned long long, select_result*, st_select_lex_unit*, st_select_lex*) (sql_select.cc:3570)

==12875==    by 0x6E055F: handle_select(THD*, LEX*, select_result*, unsigned long) (sql_select.cc:373)

==12875==    by 0x6AC2D9: execute_sqlcom_select(THD*, TABLE_LIST*) (sql_parse.cc:6399)

==12875==    by 0x6A1AE4: mysql_execute_command(THD*) (sql_parse.cc:3423)

==12875== Conditional jump or move depends on uninitialised value(s)

==12875==    at 0x9BE56B: Item_func_concat::val_str(String*) (item_strfunc.cc:648)

==12875==    by 0x93ADD6: Item::save_in_field(Field*, bool) (item.cc:6278)

==12875==    by 0x7AD13E: TABLE::update_virtual_fields(enum_vcol_update_mode) (table.cc:7354)

==12875==    by 0x91C9F8: handler::ha_index_first(unsigned char*) (handler.cc:2725)

==12875==    by 0xA7F133: get_index_min_value(TABLE*, st_table_ref*, Item_field*, unsigned int, unsigned int) (opt_sum.cc:117)

==12875==    by 0xA7FB0B: opt_sum_query(THD*, List<TABLE_LIST>&, List<Item>&, Item*) (opt_sum.cc:403)

==12875==    by 0x6E3C25: JOIN::optimize_inner() (sql_select.cc:1393)

==12875==    by 0x6E2B05: JOIN::optimize() (sql_select.cc:1076)

==12875==    by 0x6EB535: mysql_select(THD*, TABLE_LIST*, unsigned int, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, unsigned long long, select_result*, st_select_lex_unit*, st_select_lex*) (sql_select.cc:3570)

==12875==    by 0x6E055F: handle_select(THD*, LEX*, select_result*, unsigned long) (sql_select.cc:373)

==12875==    by 0x6AC2D9: execute_sqlcom_select(THD*, TABLE_LIST*) (sql_parse.cc:6399)

==12875==    by 0x6A1AE4: mysql_execute_command(THD*) (sql_parse.cc:3423)

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