return (and => [ invoice => 1, amount => { lt => 0 }, or => [ storno => 0, storno => undef ] ]) if $type eq 'credit_note';
return (and => [ invoice => 1, amount => { lt => 0 }, storno => 1 ]) if $type =~ m/(?:invoice_)?storno/;
return (and => [ invoice => 1, amount => { ge => 0 }, storno => 1 ]) if $type eq 'credit_note_storno';
+ return (amount => {gt => 'paid'}) if $type eq 'open';
die "Unknown type $type";
}