Problem with that, its all-or-nothing, if you want to isolate a single sub , you have to set $^WARNING_BITS, because the alternative is this wrapper crap

sub notFun {
    no warnings 'uninitialized';
    goto &_notFunXS;
}
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I'm not sure how a wrapper takes the "fun" out things for you. But providing a Perl wrapper for an XS function often makes using the module more fun than having to deal with the relatively brittle interfaces that get created when code is written in XS.

So I'd encourage using a wrapper, but one that not just disables one annoying warning, but one that pulls the data out of Perl-friendly structures and puts it into C-friendly structures so that your XS code can just deal with the data easily and can avoid the convoluted and complex issues of Perl reference counts and potential "magic".

So the wrapper can deal with the problem of undef using a language that makes that easy (Perl).