Treat None as NULL for explicity clearing values in the XP database

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "badgey"
-version = "3.0.0"
+version = "3.0.1"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

src/badgey/models/xp.rs

@@ -13,6 +13,7 @@ use crate::badgey::schema::*;
 #[diesel(belongs_to(UserInfo, foreign_key = user_id))]
 #[diesel(table_name = xp_table)]
 #[diesel(primary_key(user_id))]
+#[diesel(treat_none_as_null = true)]
 pub struct Xp {
     pub user_id: i64,
     pub user_current_level: i32,