bug: no error when attribute can undefined because arg?: <type>

[tachibana-shin]

Hi antfu!,

I'm using your eslint configuration and it has a very serious error for me.
It appears that this configuration has disabled the ability to recognize a value that could be undefined when it is defined with ?:

Not working:

Working:

You can see that when I specify format?: string[] then eslint does not specify format as undefined and format.forEach is still valid. But when I specify the format?: string[] | void, the format.forEach will experience an error.

Please fix,
Thanks for read!

[antfu]

We temporarily close this due to the lack of enough information. Please provide a minimal reproduction to reopen the issue. Thanks.