invalid-str-returned:36:4:37:21:FirstBadStr.__str__:__str__ does not return str:UNDEFINED
invalid-str-returned:43:4:44:16:SecondBadStr.__str__:__str__ does not return str:UNDEFINED
invalid-str-returned:50:4:51:33:ThirdBadStr.__str__:__str__ does not return str:UNDEFINED
