Multiple Parameters [SOLVED]

Unity dosnt seem happy with the way im passing the paramters and i dont understand why…

GunInventory.savedGuns.Add(GunCreator.CreateGun(name, caliber, length, rifled));

to

public static Gun CreateGun(string name, int caliber, int length, bool rifled)

I dont understand what the error itself means exactly as an all rounder. The Null error is stright forward but I dont know what this error generally means.

Ah fixed it, mismatch data type.