use 5.010;
use Moose;
use MooseX::Params::Validate;

sub test {
    my ($self, %params) = validated_hash(\@_,
        i => {isa => 'Defined',},
    );
    return "$params{i} ist immer ein definierter Wert";
}

my $obj = __PACKAGE__->new;

say $obj->test(i => 'abc');   # ok
say $obj->test(i => 0);       # ok
say $obj->test(i => undef);   # nok
say $obj->test;               # nok