Fix error due to `serial_number` being renamed to `entry`
Fix error due to `serial_number` being renamed to `entry`

In the live register TSV output, `serial_number` has been renamed to
`entry`. Prevent a field register lookup for `entry` as it does not
exist as a record in the field register.

Also fix error due to from_openregister being set to nil not false in
constructor.

robmckinnon/openregister-ruby