Hello,

As explain in the error message, product_template has a field categ_id which on is required !

categ_id = fields.Many2one(
     'product.category', 'Internal Category',
     change_default=True, default=_get_default_category_id, domain="[('type','=','normal')]",
     required=True, help="Select category for the current product")

When you start with a fresh database, you have  "product.product_category_all" as valid xml_id .... 

That's the default value when you create a product via the UI. (_get_default_category_id)

Thanks for answer