Fix problem in default_tax related to sum in active record

app/models/calculator/default_tax.rb

@@ -49,7 +49,7 @@ module Calculator
     # Finds relevant fees for each line_item,
     #   calculates the tax on them, and returns the total tax
     def per_item_fees_total(order, calculator)
-      order.line_items.sum do |line_item|
+      order.line_items.to_a.sum do |line_item|
         calculator.per_item_enterprise_fee_applicators_for(line_item.variant)
           .select { |applicator| applicable_rate?(applicator, line_item) }
           .sum { |applicator| applicator.enterprise_fee.compute_amount(line_item) }

app/models/calculator/flat_percent_per_item.rb

@@ -18,7 +18,7 @@ class Calculator::FlatPercentPerItem < Spree::Calculator
   end
 
   def compute(object)
-    line_items_for(object).sum do |li|
+    line_items_for(object).to_a.sum do |li|
       unless li.price.present? && li.quantity.present?
         raise ArgumentError, "object must respond to #price and #quantity"
       end

app/models/calculator/weight.rb

@@ -32,7 +32,7 @@ module Calculator
     private
 
     def total_weight(line_items)
-      line_items.sum do |line_item|
+      line_items.to_a.sum do |line_item|
         line_item_weight(line_item)
       end
     end

spec/features/admin/bulk_product_update_spec.rb

@@ -133,7 +133,7 @@ feature '
       expect(page).to have_selector "a.view-variants", count: 1
       all("a.view-variants").each(&:click)
 
-      expect(page).to have_selector "span[name='on_hand']", text: p1.variants.sum(&:on_hand).to_s
+      expect(page).to have_selector "span[name='on_hand']", text: p1.variants.to_a.sum(&:on_hand).to_s
       expect(page).to have_field "variant_on_hand", with: "15"
       expect(page).to have_field "variant_on_hand", with: "6"
     end