Which kind of implies that it creates a PV-type SV

...when given "a non-zero len parameter", which doesn't apply to your code. You have a gave a zero len parameter, for which its documentation only says it "Creates a new SV." It creates the most basic of SVs:

use Inline C => <<'__EOI__';

void testing() {
   SV* sv = newSV(0);
   sv_dump(sv);
   SvREFCNT_dec(sv);
}

__EOI__

testing();
[download]

SV = NULL(0x0) at 0x8eec248
  REFCNT = 1
  FLAGS = ()
[download]

This creates a PV:

newSVpvn("", 0)
[download]

I believe I::C will take care of that for me.

Yes, though it's actually XS by means of the typemap that does it.