nearly there.

In the for loop you need to skip those vm's without custom fields:

for my $vm ( sort { $a->name cmp $b->name } @$vm_view ) {
    my $cv_ref = $vm->{'summary.customValue'};
    next unless defined ( $vm->{'summary.customValue'} ) ;
    print $vm->name . "\n";
    for ( @$cv_ref ) {
        print "key: ", $_->key, "\tvalue: ", $_->value, "\n";
    }
}

o, and you need to retrieve the 'name' property of the vm as well if you copy paste that