Use of uninitialized value in sprintf

[ViktorNacht]

Running the module under perl 5.22.4 I get the following error message:

Use of uninitialized value in sprintf at /opt/perl5/perls/admin1.0/lib/site_perl/5.24.3/WebService/Prowl.pm line 74.

[brother]

Can not really wrap my head around what it fails on. Three possible errors, the @out, the $query and the $k.
https://github.com/sekimura/WebService-Prowl/blob/master/lib/WebService/Prowl.pm#L74

[brother]

While testing this further it seems like it actually does work now. Still get the annoying warning(?) about uninitialized and so on. Only things I am certain that I have done is that I have reinstalled the cpan module and restarted irssi (where I am using this from).