feat: add validation to check UPRN exists if address doesn't

app/services/bulk_upload/lettings/year2023/row_parser.rb

@@ -334,6 +334,8 @@ class BulkUpload::Lettings::Year2023::RowParser
 
   validate :validate_valid_radio_option, on: :before_log
 
+  validate :validate_uprn_exists_if_address_does_not
+
   def self.question_for_field(field)
     QUESTIONS[field]
   end
@@ -431,6 +433,12 @@ private
     @created_by ||= User.find_by(email: field_3)
   end
 
+  def validate_uprn_exists_if_address_does_not
+    if field_18.blank? && field_19.blank? && field_21.blank?
+      errors.add(:field_18, I18n.t("validations.not_answered", question: "UPRN known"))
+    end
+  end
+
   def validate_needs_type_present
     if field_4.blank?
       errors.add(:field_4, I18n.t("validations.not_answered", question: "needs type"))