CLDC-4142: Ensure description if nil if not shown

looks like there's no automated process for this. without this the description will be "" if not given

app/models/derived_variables/lettings_log_variables.rb

@@ -177,6 +177,8 @@ module DerivedVariables::LettingsLogVariables
       self.la = nil
     end
 
+    clear_gender_description! if form.start_year_2026_or_later?
+
     set_checkbox_values!
   end
 
@@ -418,6 +420,16 @@ private
     return 3 if rent_type == 5
   end
 
+  def clear_gender_description!
+    # if gender matching sex not picked as "No, enter gender identity", clear the dependent description field
+    (1..8).each do |person_index|
+      gender_same_as_sex = public_send("gender_same_as_sex#{person_index}")
+      if gender_same_as_sex.present? && gender_same_as_sex != 2
+        self["gender_description#{person_index}"] = nil
+      end
+    end
+  end
+
   def set_checkbox_values!
     form.questions.select { |q| q.type == "checkbox" }.each do |question|
       options = question.answer_keys_without_dividers