Use join to only insert space when both parts of postcode are provided

app/services/bulk_upload/lettings/year2024/row_parser.rb

@@ -1355,7 +1355,7 @@ private
   end
 
   def postcode_full
-    "#{field_21} #{field_22}" if field_21 || field_22
+    [field_21, field_22].compact_blank.join(" ") if field_21 || field_22
   end
 
   def owning_organisation

app/services/bulk_upload/sales/year2024/row_parser.rb

@@ -1074,7 +1074,7 @@ private
   end
 
   def postcode_full
-    "#{field_27} #{field_28}" if field_27 || field_28
+    [field_27, field_28].compact_blank.join(" ") if field_27 || field_28
   end
 
   def ppostcode_full

spec/services/bulk_upload/lettings/year2024/row_parser_spec.rb

@@ -2720,7 +2720,7 @@ RSpec.describe BulkUpload::Lettings::Year2024::RowParser do
       end
 
       context "when a partial postcode is provided" do
-        let(:attributes) { { bulk_upload:, field_4: 1, field_21: "EC1N", field_22: nil } }
+        let(:attributes) { { bulk_upload:, field_4: 1, field_21: "EC1N", field_22: "" } }
 
         it "is set to the partial value" do
           expect(parser.log.postcode_full).to eql("EC1N")