Product Type Variable error

using Jigoshop ecommerce 2.1.12

When I create a new product with product type simple – everything works fine.
When I create a new product with product type variable, add all the relevant information but when I try to access my Products page the following error occurs.

Call to undefined method Jigoshop\Entity\Product\Variable::getStock()

Switching back to product type simple or deleting the product resolves the error.