feat: convert empty emails to None in register form handler

SUMMARY
    Browsers send empty strings for empty fields in form submissions.
    Email is optional in registration process but empty field fails
    validation for email and results in 400 bad request. Converting
    empty strings to None fixes this.

src/pages/auth/register.rs

@@ -71,10 +71,15 @@ pub fn services(cfg: &mut web::ServiceConfig) {
 
 #[my_codegen::post(path = "PAGES.auth.register")]
 pub async fn register_submit(
-    payload: web::Form<RegisterPayload>,
+    mut payload: web::Form<RegisterPayload>,
     data: AppData,
     db: crate::DB,
 ) -> PageResult<impl Responder, Register> {
+    if let Some(email) = &payload.email {
+        if email.is_empty() {
+            payload.email = None;
+        }
+    }
     data.register(&(**db), &payload)
         .await
         .map_err(|e| PageError::new(Register::new(&data.settings, Some(&payload)), e))?;

src/pages/auth/test.rs

@@ -67,6 +67,23 @@ async fn auth_works(data: Arc<Data>, db: BoxDB) {
     assert_eq!(headers.get(header::LOCATION).unwrap(), PAGES.auth.login);
     let _ = data.delete_user(&db, NAME, PASSWORD).await;
 
+    // 1. Register with email == "" // Form request handler converts empty emails to None
+    let msg = Register {
+        username: NAME.into(),
+        password: PASSWORD.into(),
+        confirm_password: PASSWORD.into(),
+        email: Some("".into()),
+    };
+    let resp = test::call_service(
+        &app,
+        post_request!(&msg, PAGES.auth.register, FORM).to_request(),
+    )
+    .await;
+    assert_eq!(resp.status(), StatusCode::FOUND);
+    let headers = resp.headers();
+    assert_eq!(headers.get(header::LOCATION).unwrap(), PAGES.auth.login);
+    let _ = data.delete_user(&db, NAME, PASSWORD).await;
+
     // 1. Register with email
     let msg = Register {
         username: NAME.into(),