Make the _lastPayloadId a ulong and then cast id to a ulong when you set the id

So up top

```c#
private ulong? _lastPayloadId = null;
```

then in Receive

```c#
_lastPayloadId = (ulong?)lastPayloadIdOperation.ExecuteScalar();
```

and lastly then in the ProcessRecord

```c#
var id = (ulong)record.GetInt64(0);
```

Overall being a ulong by default makes more sense since our ID's will never be negative.