fix(ArrowFunction mutator): don't mutate () => undefined

[simondel]

Fixes #2306

[bartekleon]

It is so big if statement I would rather use normal "if/else" instead of ternary. It really reduces readability

[bartekleon]

And could you also check if "() => void" is mutated?

[brodybits]

[...] ternary. It really reduces readability

I think there are 2 major causes:

• using extra-large ---print-width setting in Prettier
• indenting issue that I just reported in Indentation of ternaries in return statements and function calls prettier/prettier#8741

This is really unfortunate, since I find ternaries to be much more too the point in general.

[nicojs]

✌

Can be cleanup a little, refactoring is welcome.

[rodoabad]

Yahoo! Thanks, @nicojs !

[nicojs]

Sure thing @rodoabad ! Just remember that this will be part of Stryker 4.0. I'm planning to release a new version of the beta later this week and we'll be working to a release this month or next month.