There is a regression in SvTRUE macro. Expected value is:

$ perl -MScalar::Util=dualvar -le 'print $]; $a = dualvar 1, ""; print $a ? "true" : "false";'
5.016003
false

This is broken in 5.18.0 and fixed with upstream commit:

commit 762dbf22cb22645771fc27b5d197fd40cbbd9da8
Author: Father Chrysostomos <sprout>
Date:   Sat May 25 23:59:45 2013 -0700

    [perl #118159] Make PVs take precedence in SvTRUE
    
    Commit 4bac9ae4 (probably inadvertently) changed SvTRUE to treat an SV
    with any of PVX, IVX or NVX having a true value as true.
    
    Traditionally, truth was based solely on stringification. The examina-
    tion of the SvIVX and SvNVX slots was for those cases where there was
    no string already and it could be deduced from IVX or NVX whether it
    would stringify as "0" or no (bugs with -0 aside).
    
    This changes things back to the way they have ‘always’ been.