commit 1cd9d5dc80b9142ec20649a163338180620c3674
Author: Nicolas Meyer <nicolas@commerceguys.com>
Date:   Tue Oct 2 16:15:22 2012 +0200

    Delete product type if already exist.

diff --git a/product_type.inc b/product_type.inc
index 5945019..9899744 100644
--- a/product_type.inc
+++ b/product_type.inc
@@ -57,6 +57,12 @@ class CommerceMigrateUbercartProductTypeMigration extends Migration {
     // Done here instead of in the plugin so that an UPDATE could be done by changing
     // the line bellow.
     $type->is_new = TRUE;
+
+    // If the product type that will be migrated already exist, delete it
+    // before running the migration.
+    if (array_key_exists($type->type, commerce_product_types())) {
+      commerce_product_ui_product_type_delete($type->type);
+    }
   }
 
   /**