use find_one for auth search

src/commands.rs

@@ -157,7 +157,7 @@ pub async fn add_auth_user(
     #[description = "Discord user ID"] id: String,
 ) -> Result<(), Error> {
     if !std::env::var("ADMIN_USERS")
-        .expect("missing ADMIN_USERS")
+        .unwrap_or(String::new())
         .contains(&ctx.author().id.to_string())
     {
         ctx.say("You don't have permission to add a new user")

src/database.rs

@@ -90,8 +90,7 @@ pub fn is_auth_user(discord_id: String) -> Result<bool, Error> {
         .get()
         .unwrap()
         .collection::<AuthorizedUser>("authorized_users")
-        .find(doc! { "$eq": [{"discord_id": discord_id}] })
+        .find_one(doc! { "discord_id": discord_id })
         .map_err(|err| Error::new(ErrorKind::InvalidInput, err))?
-        .next()
         .is_some())
 }