convert field_mapping to array of hashes

app/services/bulk_upload/lettings/row_parser.rb

@@ -176,25 +176,25 @@ private
   end
 
   def field_for_attribute(attribute)
-    field_mapping.invert[attribute]
+    field_mapping.find { |h| h[:attribute] == attribute }[:name]
   end
 
   def field_mapping
-    {
+    [
-      field_1: :lettype,
+      { name: :field_1, attribute: :lettype },
-      field_134: :renewal,
+      { name: :field_7, attribute: :tenancycode },
-    }
+      { name: :field_134, attribute: :renewal },
+    ]
   end
 
   def attributes_for_log
-    hash = field_mapping.invert
     attributes = {}
 
-    hash.map do |k, v|
+    field_mapping.map do |h|
-      attributes[k] = public_send(v)
+      attributes[h[:attribute]] = public_send(h[:name])
     end
 
-    hash[:scheme] = scheme
+    attributes[:scheme] = scheme
 
     attributes
   end

spec/services/bulk_upload/lettings/row_parser_spec.rb

@@ -88,6 +88,16 @@ RSpec.describe BulkUpload::Lettings::RowParser do
       end
     end
 
+    describe "#field_7" do
+      context "when null" do
+        let(:attributes) { { field_7: nil } }
+
+        xit "returns an error" do
+          expect(parser.errors[:field_7]).to be_present
+        end
+      end
+    end
+
     describe "#field_134" do
       context "when an unpermitted value" do
         let(:attributes) { { field_134: 3 } }