CLDC-3487: Use nil instead of 0

app/models/derived_variables/lettings_log_variables.rb

@@ -123,7 +123,7 @@ module DerivedVariables::LettingsLogVariables
                         0
                       end
       self.is_previous_la_inferred = is_la_inferred
-      self.previous_la_known = la.present? ? 1 : 0
+      self.previous_la_known = la.present? ? 1 : nil
       self.prevloc = la
     end
 

spec/models/lettings_log_derived_fields_spec.rb

@@ -991,7 +991,7 @@ RSpec.describe LettingsLog, type: :model do
       log.assign_attributes(postcode_known: 0, postcode_full: nil, la: nil, renewal: 1, previous_la_known: 1, prevloc: "E09000033", ppostcode_full: "SW1A 1AA", ppcodenk: 0)
 
       expect { log.set_derived_fields! }
-        .to change(log, :previous_la_known).to(0)
+        .to change(log, :previous_la_known).to(nil)
         .and change(log, :prevloc).to(nil)
         .and change(log, :ppcodenk).to(1)
         .and change(log, :ppostcode_full).to(nil)