Fixed static analysis issues.

src/Repository/AbstractPartsContainingRepository.php

@@ -33,7 +33,7 @@ abstract class AbstractPartsContainingRepository extends StructuralDBElementRepo
      * @param  object  $element  the element for which the parts should be determined
      * @param  array  $order_by  The order of the parts. Format ['name' => 'ASC']
      *
-     * @return Part
+     * @return Part[]
      */
     abstract public function getParts(object $element, array $order_by = ['name' => 'ASC']): array;