Invalid services config: service[selectuserbooks] return_type is mandatory

stack traceback:
    /home/centos/work/tdg/common/config_checks.lua:10: in function 'assert'
    /home/centos/work/tdg/input_processor/services/config.lua:39: in function 'validate_service'
    /home/centos/work/tdg/input_processor/services/config.lua:71: in function </home/centos/work/tdg/input_processor/services/config.lua:62>
    [C]: in function 'pcall'
    /home/centos/work/tdg/input_processor/services/config.lua:89: in function 'validate'
    /home/centos/work/tdg/input_processor/config.lua:141: in function </home/centos/work/tdg/input_processor/config.lua:45>
    [C]: in function 'pcall'
    /home/centos/work/tdg/input_processor/config.lua:152: in function </home/centos/work/tdg/input_processor/config.lua:151>
    [C]: in function 'xpcall'
    /home/centos/work/tdg/.rocks/share/tarantool/errors.lua:145: in function 'pcall'
    ...ntos/work/tdg/.rocks/share/tarantool/cartridge/roles.lua:257: in function 'validate_config'
    ...s/work/tdg/.rocks/share/tarantool/cartridge/twophase.lua:52: in function <...s/work/tdg/.rocks/share/tarantool/cartridge/twophase.lua:49>
    [C]: in function 'xpcall'
    /home/centos/work/tdg/.rocks/share/tarantool/errors.lua:145: in function </home/centos/work/tdg/.rocks/share/tarantool/errors.lua:139>
    [C]: in function 'xpcall'
    /home/centos/work/tdg/.rocks/share/tarantool/errors.lua:145: in function 'pcall'
    /home/centos/work/tdg/common/netbox_monkeypatch.lua:57: in function </home/centos/work/tdg/common/netbox_monkeypatch.lua:51>
    [C]: at 0x005acf70
during net.box call to localhost:3301, function "__netbox_call_with_fiber_storage"
stack traceback:
    [C]: in function 'xpcall'
    /home/centos/work/tdg/.rocks/share/tarantool/errors.lua:145: in function 'pcall'
    /home/centos/work/tdg/.rocks/share/tarantool/errors.lua:372: in function 'netbox_call'
    ...entos/work/tdg/.rocks/share/tarantool/cartridge/pool.lua:151: in function <...entos/work/tdg/.rocks/share/tarantool/cartridge/pool.lua:141>