FIX : We must remove empty values of $features array in fetchByProductCombination2ValuePairs() because some products can use only several attributes in their variations and not necessarily all. In this case, fetch doesn't work without my correction

htdocs/variants/class/ProductCombination.class.php

@@ -602,6 +602,8 @@ class ProductCombination
 		$prodcomb2val = new ProductCombination2ValuePair($this->db);
 		$prodcomb = new ProductCombination($this->db);
 
+		$features = array_filter($features);
+
 		foreach ($features as $attr => $attr_val) {
 			$actual_comp[$attr] = $attr_val;
 		}