+----------+------------------+
| clientip | clientip_country |
+----------+------------------+
|  8.8.8.8 | null             |
|  1.1.1.1 | null             |
|  4.4.4.4 | null             |
+----------+------------------+

+----------+------------------+
| clientip | clientip_country |
+----------+------------------+
|  8.8.8.8 | US               |
|  1.1.1.1 | AU               |
|  4.4.4.4 | US               |
+----------+------------------+

$ mmdblookup -f /usr/share/GeoIP/GeoLite2-Country.mmdb -i 1.1.1.1 country iso_code | sed -e '/^$/d' -e 's/.*"(.*)".*/1/'
AU