Commerce feeds with xpath parser returns SQLSTATE[42000] with an XML file with 2 products

I am using commerce_feeds 7.x-1.x-dev with feeds 7.x-2.x-dev and feeds_xpathparser 7.x-1.x-dev.

I created an XML product importer. Importing an XML file with 1 product works as expected. Importing an XML with 2 products returns a SQLSTATE[42000]: Syntax error or access violation: 1064 error.

Importing a CSV file with 2 products works as expected.

This bug has also been noticed in issue queue `Feeds Xpath Parser` at http://drupal.org/node/1314326 although it has been closed the problem still exists and the works as expected is not true.

I debugged the problem and I attached some screenshots to demonstrate the error.

The problem lies in function `FeedsCommerceProductProcessor.existingEntityId().

The SQL query is constructed:

$product_id = db_query("SELECT product_id FROM {commerce_product} WHERE sku = :sku", array(':sku' => $value))->fetchField();

But the $value parameter is an array of 2 elements (in case of xpath parser) and the construction of the mysql query is wrong.

Although I am an experienced programmer, I am a Drupal newbie with not enough module flow knowledge to fix the error. The problem lies in a difference between the parsed result from a feeds CSV and feeds XPATH importer. The function `FeedsCommerceProductProcessor.uniqueTargets()` returns different results for different importers.