refac: several unverified users can exist at once: an empty reset or verification code is stored as no value so it doesn't break the unique constraint, and deleting a user removes the row so the same username and email can register again

internal/infrastructure/persistence/repositories/userRepository.go

@@ -30,8 +30,9 @@ func (u *UserRepository) Create(user domainUser.User) (domainUser.User, error) {
 	creationResult := u.db.Create(&entity.User{
 		Username:               user.Username,
 		Password:               user.Password,
+		PasswordResetCode:      mappers.DomainToNullableString(user.PasswordResetCode),
 		Email:                  user.Email,
-		VerificationCode:       user.VerificationCode,
+		VerificationCode:       mappers.DomainToNullableString(user.VerificationCode),
 		VerificationExpiration: user.VerificationExpiration,
 	})
 	if creationResult.Error != nil {
@@ -121,7 +122,7 @@ func (u *UserRepository) UpdatePasswordResetCode(userId uint32, code string) (do
 		return domainUser.User{}, mapNotFoundErr(err, domainUser.ErrUserNotFound)
 	}
 
-	localUser.PasswordResetCode = code
+	localUser.PasswordResetCode = mappers.DomainToNullableString(code)
 	err = u.db.Save(&localUser).Error
 	if err != nil {
 		return domainUser.User{}, err