Problem importing worlds using API

[MurrenMods]

I might be missing something simple, so dont flame me too much:

When trying to import worlds using
p.importWorld(File, Name, Loader)
my plugin throws the error 'loader cannot be null'.
This refers to the Loader in that function, which I earlier defined as

static SlimePlugin p = (SlimePlugin) Bukkit.getPluginManager().getPlugin("SlimeWorldManager");
static SlimeLoader l = p.getLoader("mysql");

Do I need to install anything? Like, mysql software or something similar? My code doesn't throw any other errors, it just cant make the loader anything different than null.

EDIT: Solved, i was too stupid to catch on what the data source actually meant. File System works amazing, and i can convert my worlds now. Thanks for this amazing plugin!