Filter::OP_EXISTS and OP_NOT_EXISTS are the wrong way round

see Filter.php line 82ff.

`case self::OP_EXISTS:
    $params[] = $filter[0] . '=';
    break;
case self::OP_NOT_EXISTS:
    $params[] = $filter[0] . '!=';
    break;
`

In redis docs https://redis.io/commands/ts.mrange/:

`label=`, where key does not have label label
`label!=`, where key has label label