Meaning of happy-go-lucky

[Rich7]

Test No. incompl/inter-93 "Hotchpotch", question 4

He's the sort of person who never worries about anything and has a happy ......... disposition.

(a) over-heels
(b) tempered
(c) disposed
(d) go-lucky

Test No. incompl/inter-93 "Hotchpotch", answer 4

He's the sort of person who never worries about anything and has a happy go-lucky disposition.

Correct answer: (d) go-lucky

Your answer was: incorrect
He's the sort of person who never worries about anything and has a happy tempered disposition.
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go lucky disposition? please expain...
Also, what happens when I lose the dash here?

[Torsten]

Happy go-lucky (or happy-go-lucky) is an adjective meaning carefree, free of responsibilities, cheerful. It's usually written with one or even two hyphens for more clarity.

TOEFL listening discussions: A conversation between two students in their first class of the term

[Rich7]

Kind of American "easy going" isn't it?