Make net income frequency not required dynamically

No errors need to be added if the net income is given as 0 but no frequency
is provided. It just needs to be made not required if the net income is
refused (given as 0) so that the record can still be added.

app/models/case_log.rb

@@ -105,6 +105,10 @@ private
       dynamically_not_required << "other_reason_for_leaving_last_settled_home"
     end
 
+    if net_income.to_i == 0
+     dynamically_not_required << "net_income_frequency" 
+    end
+
     required.delete_if { |key, _value| dynamically_not_required.include?(key) }
   end
 end

spec/fixtures/complete_case_log.json

@@ -68,8 +68,8 @@
       "property_major_repairs_date": "05/05/2020",
       "property_number_of_times_relet": 2,
       "property_wheelchair_accessible": true,
-      "net_income": 1000,
+      "net_income": 0,
-      "net_income_frequency": "Monthly",
+      "net_income_frequency": null,
       "net_income_uc_proportion": "Some",
       "housing_benefit": "Universal Credit with housing element, but not Housing Benefit",
       "rent_frequency": "Weekly",