minor: Fix undef as array ref error in perl < 5.22
minor: Fix undef as array ref error in perl < 5.22

dagolden/mongo-perl-driver,dagolden/mongo-perl-driver,xdg/mongo-perl-driver,mongodb/mongo-perl-driver,mongodb/mongo-perl-driver,dagolden/mongo-perl-driver,mongodb/mongo-perl-driver,xdg/mongo-perl-driver,xdg/mongo-perl-driver,dagolden/mongo-perl-driver