# THIS DOESN'T WORK:

my $versione_nota = $dbic->resultset('VersioneNotaLt')->search({
        ser_num => $ser_num, mdsrel_id_req => $mdsrel_id_req})->count();

# THIS WORKS FINE:
my @versione_nota_set = $dbic->resultset('VersioneNotaLt')->search({
        ser_num => $ser_num, mdsrel_id_req => $mdsrel_id_req});
my $versione_nota = $#versione_nota_set;