fixup! CLDC-4142: Ensure description if nil if not shown

update inferral method name and comment

app/models/derived_variables/lettings_log_variables.rb

@@ -177,7 +177,7 @@ module DerivedVariables::LettingsLogVariables
       self.la = nil
     end
 
-    clear_gender_description! if form.start_year_2026_or_later?
+    clear_gender_description_unless_gender_not_same_as_sex! if form.start_year_2026_or_later?
 
     set_checkbox_values!
   end
@@ -420,8 +420,10 @@ private
     return 3 if rent_type == 5
   end
 
-  def clear_gender_description!
+  def clear_gender_description_unless_gender_not_same_as_sex!
-    # if gender matching sex not picked as "No, enter gender identity", clear the dependent description field
+    # we do this as the gender same as sex page always contains the gender description box that's hidden
+    # default submit will send a "" for gender description. this ensure it's nil in this case
+    # as well as blanking it if the user writes it in mistakenly in bulk upload
     (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