Import product's invalid weight as 1 item

We previously stored a scale which made the product screen believe that
we are dealing with weight.

engines/dfc_provider/app/services/quantitative_value_builder.rb

@@ -31,12 +31,16 @@ class QuantitativeValueBuilder < DfcBuilder
     measure, unit_name, unit_scale = map_unit(quantity.unit)
     value = quantity.value.to_f * unit_scale
 
+    # Import invalid value as one item.
     if measure.in?(%w(weight volume)) && value <= 0
       measure = "items"
       unit_name = "items"
       value = 1
     end
 
+    # Items don't have a scale, only a value on the variant.
+    unit_scale = nil if measure == "items"
+
     product.variant_unit = measure
     product.variant_unit_name = unit_name if measure == "items"
     product.variant_unit_scale = unit_scale

engines/dfc_provider/spec/services/quantitative_value_builder_spec.rb

@@ -58,7 +58,7 @@ RSpec.describe QuantitativeValueBuilder do
 
       expect(product.variant_unit).to eq "items"
       expect(product.variant_unit_name).to eq "Jar"
-      expect(product.variant_unit_scale).to eq 1
+      expect(product.variant_unit_scale).to eq nil
       expect(product.unit_value).to eq 3
     end
 
@@ -142,7 +142,7 @@ RSpec.describe QuantitativeValueBuilder do
 
       expect(product.variant_unit).to eq "items"
       expect(product.variant_unit_name).to eq "dozen"
-      expect(product.variant_unit_scale).to eq 12
+      expect(product.variant_unit_scale).to eq nil
       expect(product.unit_value).to eq 24
     end
   end

engines/dfc_provider/spec/services/supplied_product_builder_spec.rb

@@ -107,6 +107,8 @@ RSpec.describe SuppliedProductBuilder do
       expect(subject).to be_persisted
       expect(subject.name).to eq("Fillet Steak - 201g x 1 Steak")
       expect(subject.variant_unit).to eq("items")
+      expect(subject.product.variant_unit_scale).to eq(nil)
+      expect(subject.product.variant_unit_with_scale).to eq("items")
       expect(subject.unit_value).to eq(1)
     end
   end