migrate variants with nil unit_value

db/migrate/20210202052337_migrate_variant_unit_values.rb

@@ -0,0 +1,13 @@
+class MigrateVariantUnitValues < ActiveRecord::Migration
+  def up
+    Spree::Variant.all.select { |v|
+      v.unit_value.nil? && v.product&.variant_unit == "items"
+    }.each do |variant|
+      variant.unit_value = 1
+      variant.save
+    end
+  end
+
+  def down
+  end
+end